I think the thing with Carey is that you have to assume that if he's here, then it's as the 17th forward and you're probably in pretty bad shape if you're forced to use him. You'd basically need to have lost half your forwards for him to be in the lineup. If that 17th forward is basically your 'break glass in case of emergency' option, then you probably want some versatility (which he offers), so I get keeping him around.
The thing going against him is that of all of the players in training camp, he's played the fewest number of NHL games this year (1), so it's clear they value others more. Personally, I'd rather take the question mark in one of the younger players who could step up in the playoffs over a AAAA player in Carey. We know for a fact that Carey is not an NHL player in the regular season, so why would we want him in there in the playoffs? We still don't have that answer for the other players on the supposed "bubble". Hopefully that 17th forward isn't going to play anyway, so maybe they can get some valuable development time.