It's pretty trivial to convert from BTC to Monero and back. There are even services that will send a specific address BTC automatically if you send them Monero.

It's pretty trivial to convert from BTC to Monero and back. There are even services that will send a specific address BTC automatically if you send them Monero. So unless the exchange is going to ban mixed coins and Monero-based sources, that won't lead to Orwellian-style undodgeable monitoring of every transaction. It's an option to do that, of course, but it would be precedent-setting. No one else bans BTC that came in via a Monero service.