Security - View only user

When you say "View Only" access, that can be interpreted as View Only data or View Only metadata.  I'm assuming from the rest of your question, you are trying to give a subset of users access to see metadata Dimension members in the Dimension Library.  

1st step is to give the users in the security groups access to the DimensionLibraryPage

2nd step is to give them access to the individual Dimension objects that you want to grant access to.  This security is controlled on the DImensions itself under Dimension Properties.  There is an Access and Maintenance Group for each Dimension.  So Administrators and/or Power Users should only have access to Maintenance Group.  The Access Group is the security group that those subset of users should have access to.  

Side note - The ManageMetadata security role gives users the access rights to access and maintain all Metadata objects.  So getting access to this group would trump any other security you would have on the Dimensions. 

Recap - Give access to DimensionLibraryPage, set security group on Access Group for each Dimension under Dimension Properties, and assign user to security group assigned to Access Group for each Dimension.  Access to ManageMetadata will give users Access and Maintenance rights for all Dimensions and Dimension members. 

If this doesn't work and you do not get anymore responses, I recommend that you submit a ticket to OneStream support.  There may be other pieces to your security model that may require more attention.