Since BadChooChoo and I pass each other quite often, I know what Choo is talking about.
PIT has hired rent-a-cops to perform this function at odd times, but they seem to be most interested in the PSA operation at the airport. I have not seen these guys checking any of the other airlines that use PIT. The WN people seem to be immune to the searches altogether from my vantage point in the terminal.
I doubt that weapons and drugs are flowing from the A-concourse in Pittsburgh, but that seems to be the excuse for checking personnel leaving US Airways Express' breakroom. Actually, if someone did have a weapon when they exited for the end of their shift, the rent-a-cops would be horribly outmatched: The r-a-c's don't appear to have any weapons and the Express people are in very good physical shape for the most part. Failing that, I'm sure the r-a-c's would easily give in for a fix.
It would appear that the best way to check the employees would be to disallow airlines other than US from entering the SIDA areas from their baggage claim areas. US employees either aren't allowed or are subject to search. OA's do not seem to be subject to the same treatment in PIT.