Bittrex is owned and operated by US actors. You can go talk to them in their slack. They're on their with their real names, and they all have linkedin profiles with real work histories at US companies.

Poloniex is owned by a guy named Tristan D'Agosta. He's a little bit less easy to track down, but does seem to be a real, known person with a real history and life.

I don't know how they each separate customer and operating funds, but i'm sure the Bittrex guys at least would probably be happy to tell you if you ask in their Slack channel, assuming they don't consider it a security risk.