Do you feel there is a big maintenance savings by doing this? One thing I think might be an issue is network traffic. If SP databases and TABLE databases are on different servers could you be generating twice the network traffic? Or if on same server, could you be consuming more memory resources on server (or tempdb).
Normally web server queries database server and database server returns data to web server. Now you have web server query SP database, which queries TABLE database, which returns data to SP database, which finally returns data to web server.
Possibly this isn't an issue, but my instinct tells me that there could be resources overhead to do it as you designed.