We occasionally used our catcher(s) on our travel team (been together 12U-16U) to pitch. But it was mostly mop up innings in a tourney. We also made sure they were fairly well rested before and after pitching.
Personally I don't think its a great idea to have your primary catcher(s) also be one of your main pitchers.
BTW, I should add that the catchers no longer pitch now that we are playing at the HS level.