Its not just about Martin's performance while catching Dickey though, you have to weigh the extra injury risk of him catching Dickey. Martin said he jammed his thumb a couple times since he can't catch the ball on the sweet spot like a conventional pitcher.
I'd rather use Thole and give Martin the best chance of being healthy/productive than get a backup catcher who might add an extra 3-4 runs over the course of the season. I think there is too much risk letting Martin catch Dickey 30 times, personally.