Another real-life example:

Did you see the Rams game a few weeks back? When PK Jeff Wilkins got hurt and the Rams had no backup kicker? They had to use a WR to kick the ball....and he did pretty damn good. Or what about a WR or HB that occasionally throws a TD pass on a flee flicker? If this was an NFL sim, that WR wouldn't be rated as a "kicker" and that HB wouldn't be rated as a QB. However, most professional athletes are just that....PROFESSIONAL athletes. Most of them can dunk a basketball. Michael Jordan dabbled with baseball, and could probably played as a NFL WR or in his earlier days. Alot of players in the NHL have probably never played as a goaltender, but if they had to in a pinch, they could probably do an okay job. My point is that catching a baseball is not rocket science. Most 8yr olds can put on catching gear and manage. Delino Deshields doesn't have a gun for an arm, and isn't even good defensively, but I would be willing to bet that if the Orioles really needed him to catch a game, he wouldn't do all that bad. I can see the simulation giving a heavy penalty for using a non-rated catcher, but not so much that the subsitute couldn't catch the ball or occasionally throw out a baserunner.