Nah, I just wouldn't risk without holding the bitcoin myself and using an exchange with a real history. I dont trust these exchanges, I dont care who backs them, unless its a soverign state. I have seen just too many exchanges dissapear overnight and clients be left holding the bag to pick up nickels in front of a steamroller. The CME is too big to fail and the US Treasury knows it, so they would back any clearing issues. I also know a thing or two about safely storing the coins myself
Then I really would not do it. Your risk is not the exchange then, but the unpredictability of IBKR and their shit margin rules and customer service.
I can tell you a couple of stories about IB...in 2008 their data feed freaked out which resulted in a couple of long positions being marked to market at a price of zero. Entire 6 figure portfolio was 6 figures in the red and it took a week until I got to someone who was qualified enough to figure out what has happened.
Not the worst week of my life, but at least top 5. IBKR, never again.
If you use real crypto exchanges, you can post only 10% - 20% of your carry trade as margin. In case they blow up, you lose very little. You will have to manage your margin level correctly, tho.
A basis trade in BTC is never a fire and forget thing, you have to check at least once a day.
But let's be honest: This position probably outperforms the return of 99% of all ET users