If you like stats, Marc Hulet, of Fangraphs, breaks down the existing situation of the Marlins catchers, offensively.
You can read it by clicking on the following link:
Personally, I think there is a lot more to catching than just hitting. However, if all things are equal defensively, or at least close, hitting must come into play.
It is an interesting run through the organization and well worth the read. Oh, in case you were wondering why there are a large number of non-roster catcher invitees to camp...someone needs to catch the pitchers as they go through their drills. It happens every spring, at least until the minor league camp opens and then some move to the minor league camp where they are needed to catch the pitchers there.