No problem and if he didn't have this pain / injury then he wouldn't be a good catcher or he wouldn't be catching good pitchers. This is a very common thing for catchers but the new stuff / keeping mitt in shape really helps to prevent the injury.
As for the rice bucket take a bucket like the 3 gallon bucket you put baseballs in. Fill it about 3/4 full of rice. Sit in a chair with the bucket between feet / legs. Take his hand and use his fingers to work his hand down to the bottom of the bucket through the rice. Once you touch the bottom then pull hand out and then do the other hand - need to use both to keep both arms / hands equal - plus this helps with bat speed / power.
How it works is your using the muscles in the hands / forearms to work the fingers through rice. It really builds up the strength in the hands / forearms. This is helpful in catching because a strong hand is less likely to get hurt. Plus it helps with sticking pitches like the low / outside fastball that tends to jerk the catchers arm back.
Plus it helps with hitting in that there will be less recoil (not sure if that is a great word to describe that action) when the ball hits the bat.