pro players dont have a problem holding some coin or usd on a sportsbook
You can also withdraw everyday from many sportsbooks so there is not a good reason to pay fees when you bet, when you win, and then on top of that pay a spread for using a bitcoin sportsbook, no pro in their right mind would do that.
Here only discuss sportsbook, balance hold in btc.
If bet in usd, I of couse go to betting broker, higher odds, higher stake.
But it was not the scope of this post discussion.