I don't have a hand condition, but the last time I did an exam at Prometric, the fingerprint scan didn't seem to work for me. Every time I left the room and came back, they'd try multiple times and ultimately would let me back in when unsuccessful at getting my print to take after I'd show my ID.
I would suggest pointing out the issue when you check in, but I doubt there's anything you can do ahead of time. It's also possible that any scarring or peels or whatever will look unique enough on the scanner to give them something usable for the day, even if not a true fingerprint.