Bittrex will allow you to deposit FIAT to them.
Provided you're willing to send more than 100K USD. They will exchange to USDT on 1:1 basis.
This does not concern me as i don't have that type of usd money wire to send. But does this still apply?
Why can't bittrex accept smaller amounts like 2k or 3k or maybe 10k usd then? 100k usd... very few people have that type of money.