It's possible if you use a SQL database application that supports an ESS link (Extended SQL Source) via ODBC to the application. Some applications support this and others don't. I forget the current list for that so I can't just post it here. WIth that connection, you can "repoint" the table occurrences in Manage | Database | Relationships to access the tables in the SQL database and then FileMaker functions as the "front end" application for that database.
So, in theory, this is quite possible, but not something to do without some careful research.