Yes, sadly, Mind Control can miss. Even after a Mind Soothe. :P Fortunately, the raid group I was with was very understanding about it. THEN they warned me I might want to put on my Shadow gear. :)
As for Naxx10 ... my guild still runs it from time to time for grins. And you don't need priests MC'ing in the 10 man version. Only the 25. 10 man has these nice little pedestal's to use. Looking back on it, for some reason, that fight and the 4H fight are the only 2 that we use 3 healers on. :P Everything else is 2 healers only. Mostly 'cause our DPS suck and need the extra oomph that a 6th DPS will give 'em. Sadly, it's one of our more competatent DPS that switches to Resto to be our 3rd healer.