Does anyone knows if there are BTC based accounts with btcc.com or I can use only USDT?
No, unfortunately there are no btc based accounts, but there are only usdt ones.
yea, there are only usdt based accounts, but in my opinion it is the most flexible and fastest option to use for wallets. You can also credit your account with fiat and then buy usdt through their exchange. I dont think that fees are too high.