I have climbed for 12 years and played the piano all that time with no problem at all. You can play the piano with callouses however I haven't had callouses for a long time which is because I work with waxes and creams when massaging since becomming a physio. Prior to that when I did have callouses I found no problem playing. And personally I'v always found climbing beneficial for my playing because the exercise always helped me to relax the finger muscles allowing them to move quickly... this may not be the same for everyone however.