Well, I've got two answers to that. One, they didn't actually make the trade so it's not certain exactly what their feelings are about Kottaras, and two, having Salty doesn't necessarily mean that they don't trust Kottaras. You can have more than one catcher at a time on a roster.
Personally my guess is that the Sox explored the idea of trading for a guy who was a bit more of a sure thing, but had no compunction about going to Kot if the price wasn't right.
Personally, and this is mostly a gut reaction, I think Kottaras hits OK this year, impresses with the glove, and makes a serious bid to stay in the big leagues. I dunno if he can become a catcher of the future, but I can't rule it out any more than I can rule out the possibility that he goes bust.