I'm trying to combine two separate Role-based security tables into one. I'm doing ok so far, but I'm just wondering what the us_data column is for in the SFSUsers table?

This is an encrypted field that contains a lot of logic, including the encrypted password and password history.

can I append that field to the same type of field in another table and retain the integrity of it?

No.  It will kill it and all of the users will no longer be able to log-in.  You are better off creating your own users preferences table rather than playing or trying to maintain this data. WE don't even do this in our medical software.  We have a user preferences table and we pull from this when the CurrentUserChanged event is fired.

Thanks.