Can a large data pivot grid pull from multiple tables?

Yes but in the settings you can only have one table. You'd have to create a table custom or BI Blend that merges data from a sql query to that table. I think what you'd do is have a SQL data adapter querying the multiple tables and you'll have to join them by a key field then that data adapter table name is the table name on the Large Data Pivot Grid. how much data is it because large data pivot grids it states have generally acceptable performance for 2-4 million records. If your data set is under a million you could look at using a Pivot Grid with a sql data adapter and assign the data adapter.

design for pivot grid components says its should be used for record counts around 100K and under. also a correction on the above. i believe for the large data pivot grid you'd need an actual table name, not sure if you can use a data adapter results table name because you don't add a data adapter to a large data pivot grid component like you would on a pivot grid.

both pivot grids and large data pivot grids have a design consideration section with recommended data volume use cases.