Combining/Joining DataSets

sry about that, here's an update, Monday morning, I misread your initial code...
Here's how you can combine the results, using what you had:

Imports System
Imports System.Collections.Generic
Imports System.Data
Imports System.Data.Common
Imports System.Globalization
Imports System.IO
Imports System.Linq
Imports System.Windows.Forms
Imports Microsoft.VisualBasic
Imports OneStream.Finance.Database
Imports OneStream.Finance.Engine
Imports OneStream.Shared.Common
Imports OneStream.Shared.Database
Imports OneStream.Shared.Engine
Imports OneStream.Shared.Wcf
Imports OneStream.Stage.Database
Imports OneStream.Stage.Engine

Namespace OneStream.BusinessRule.DashboardDataSet.GetWFStatusandCertification
    Public Class MainClass
        Public Function Main(ByVal si As SessionInfo, ByVal globals As BRGlobals, ByVal api As Object, ByVal args As DashboardDataSetArgs) As Object
            Try
                Select Case args.FunctionType

                    Case Is = DashboardDataSetFunctionType.GetDataSetNames
                        Dim DSnames As New List(Of String)()
                        DSnames.Add("GetWFStatusandCertificationF")
                        Return DSnames

                    Case Is = DashboardDataSetFunctionType.GetDataSet
                        If args.DataSetName.XFEqualsIgnoreCase("GetWFStatusandCertificationF") Then
                            Return GetWFStatusandCertificationF(si, args)
                        End If

                End Select
                Return Nothing
            Catch ex As Exception
                Throw ErrorHandler.LogWrite(si, New XFException(si, ex))
            End Try
        End Function

        Private Function GetWFStatusandCertificationF(ByVal si As SessionInfo, ByVal args As DashboardDataSetArgs) As DataTable
            Dim WFTable As New DataTable("WFSTATUS")
            Dim CertTable2 As New DataTable("WFCertSTATUS2")
            Dim CombinedTable As New DataTable("CombinedWFandCertStatus")

            CombinedTable.Columns.Add("ProfileKey")
            CombinedTable.Columns.Add("ProfileName")
            CombinedTable.Columns.Add("ScenarioName")
            CombinedTable.Columns.Add("TimeName")
            CombinedTable.Columns.Add("StatusText")
            CombinedTable.Columns.Add("LastExecutedStepStatus")
            CombinedTable.Columns.Add("LastExecutedStepTimeUTC")
            CombinedTable.Columns.Add("LastExecutedStepTimeEST")
            CombinedTable.Columns.Add("SignOffState")
            CombinedTable.Columns.Add("UserName")
            CombinedTable.Columns.Add("TimeStamp")

            Dim WFName As String = "P1000 Prudential Group"
            Dim WFScenario As String = "Actuals"
            Dim WFTime As String = "2023M12"
            Dim methodTypeId As String = XFCommandMethodTypeId.WorkflowStatus
            Dim resultDataTableName As String = "WFSTATUS"
            Dim methodQuery As String
            Dim customSubVars As New Dictionary(Of String, String)

            methodQuery = "{" & WFName & "}{" & WFScenario & "}{" & WFTime & "}{AllProfiles}{Descendants}{}"
            Using dbConnApp As DBConnInfo = BRApi.Database.CreateApplicationDbConnInfo(si)
                Dim objDataSet As DataSet = BRApi.Database.ExecuteMethodCommand(dbConnApp, methodTypeId, methodQuery, resultDataTableName, customSubVars)
                For Each row As DataRow In objDataSet.Tables("WFSTATUS").Rows
                    WFTable.Rows.Add(row.Item("ProfileKey"), row.Item("ProfileName"), row.Item("ScenarioName"), row.Item("TimeName"), row.Item("StatusText"), row.Item("LastExecutedStepStatus"), row.Item("LastExecutedStepTime"), row.Item("LastExecutedStepTime"))
                Next
            End Using

            methodTypeId = XFCommandMethodTypeId.CertificationForWorkflowUnit
            methodQuery = "{" & WFName & "}" & "{" & WFScenario & "}" & "{" & WFTime & "}" & "{True}" & "{}"
            Using DBConnAppForCert2 As DbConnInfo = BRApi.Database.CreateApplicationDbConnInfo(si)
                CertTable2.Columns.Add("ProfileKey")
                CertTable2.Columns.Add("ScenarioKey")
                CertTable2.Columns.Add("TimeKey")
                CertTable2.Columns.Add("SignOffState")
                CertTable2.Columns.Add("UserName")
                CertTable2.Columns.Add("TimeStamp")

                Dim objDataSet As DataSet = BRApi.Database.ExecuteMethodCommand(DBConnAppForCert2, methodTypeId, methodQuery, "WFCertSTATUS2", customSubVars)
                For Each row As DataRow In objDataSet.Tables("WFCertSTATUS2_SignOffGroups").Rows
                    CertTable2.Rows.Add(row.Item("ProfileKey"), row.Item("ScenarioKey"), row.Item("TimeKey"), row.Item("SignOffState"), row.Item("UserName"), row.Item("TimeStamp"))
                Next
            End Using

            For Each wfRow As DataRow In WFTable.Rows
                Dim profileKey As Object = wfRow("ProfileKey")

                Dim certRows As DataRow() = CertTable2.Select("ProfileKey = '" & profileKey.ToString() & "'")

                For Each certRow As DataRow In certRows
                    Dim newRow As DataRow = CombinedTable.NewRow()

                    newRow("ProfileKey") = wfRow("ProfileKey")
                    newRow("ProfileName") = wfRow("ProfileName")
                    newRow("ScenarioName") = wfRow("ScenarioName")
                    newRow("TimeName") = wfRow("TimeName")
                    newRow("StatusText") = wfRow("StatusText")
                    newRow("LastExecutedStepStatus") = wfRow("LastExecutedStepStatus")
                    newRow("LastExecutedStepTimeUTC") = wfRow("LastExecutedStepTimeUTC")
                    newRow("LastExecutedStepTimeEST") = wfRow("LastExecutedStepTimeEST")

                    newRow("SignOffState") = certRow("SignOffState")
                    newRow("UserName") = certRow("UserName")
                    newRow("TimeStamp") = certRow("TimeStamp")

                    CombinedTable.Rows.Add(newRow)
                Next
            Next

            Return CombinedTable
        End Function
    End Class
End Namespace