FTs catalog in SQL Server for multiple FT index
Yes, you may add several FTS indexes to a single catalog, but a full text index can only be in a single catalog. Since a full text catalog is a database object, all indexes also have to be in the same database.

If you put all of the full text indexes for a database into a single full text catalog, a catalog reorganization will cover all of the indexes in the catalog.  This is usually fine unless your indexes are quite large.  

The SQL Server Books Online describe the CREATE FULLTEXT INDEX here:
http://technet.microsoft.com/en-us/library/ms187317.aspx

If you desire to reorganize one table at a time, then you would want to use a catalog per table.