It might be. Just because you don't see any problems with having you not rotate to the other stations doesn't mean the employer doesn't see some.
But let's back up a step. Have you formally requested an accomodation under the ADA from your employer? Or have you just assumed that because your employer knows about your condition, they are already on notice that you need one? (HINT: Their knowing about your medical condition is not, in most cases, sufficient to invoke the ADA.)

