I don't think there's a DB capability builtin but what you could do is build a web services application in php/aspx,etc to do the db lookup and any logic you want to implement. you can return a simple 0 or 1 as result.
To make calls from your TCL script to this service, you'd use httpios::geturl procedure, passing in the DID you want to compare in a query string. the results of the call will determine if you want to hang up or proceed.

standard Tcl "file" and "clock" command can still be used in Cisco Tcl IVR API, so I think you should be able to do that. Just you need to watch the performance i.e. how frequent you want to write the file