I do not know if the practice of using 100 dollar bills in bigger games is, but definitely in the 1990s/early 2000s I was in a decent-sized NL game during the WSOP and I was involved in pots in which there were a mixture of chips and 100s. I was concerned at the time but there was nothing I could do. I ended up winning and went to the cashier as soon as I could to both cash in the chips and I think separately buy chips with the 100s. It turns out none of the 100s were counterfeit (or at least none were detected) but a 1000 chip was from another casino and Binion's would not cash it -- I had to take a cab to the Bellagio to cash it in and at least it turned out to be good.
But it sure seems like poker games would be a perfect place to pass counterfeit bills (if they still allow this) and counterfeit chips unless there are currently electronic counter measures taken.
In the case of the "foreign" chip, maybe I should have paid closer attention and rejected it but I sure don't recall noticing -- it was a pretty big pot and I was focusing on playing.