I ride a lot, I used to race, and I’ve got a severe-to-profound loss and wear BTEs.
If you take up racing, you’ll suffer, I hope you know that already. (But you can get a lot of joy out of it too.)
Wind noise is a big problem for me; I just really can’t talk with people above 17mph or so. The thing I’ve noticed is that hair makes a big difference. I used to wear my hair long, and that offered some shielding for my hearing aids; now that it’s often short it’s often a much bigger problem.
I’ve not had much trouble with sweat on the hearing aids themselves; the problem I have is that I get moisture beading up in the mold tubing and blocking it, which is annoying, but doesn’t seem so harmful to the aid itself. I’ve also occasionally ridden on very rainy days (fun, sometimes) and had my hearing aids stop working because of the water. I take the batteries out and let them dry out when they get home and so far they’ve been OK.
The only time I’ve had a hearing aid come off was one time I crossed somebody’s back wheel, went down, and the hearing aid popped off the earhook, which had a ball-and-socket arrangement. A car (or maybe another rider) then promptly ran over it before I found it and squished it quite badly; I took it in and was charged $200 or $250 to “repair” it (it was a complete new aid). These were old hearing aids, and all the aids I’ve seen since had a much more secure arrangement.