Jordany Valdespin and Kirk Nieuwenhuis also made the team as backups.
According to Adam Rubin of ESPN New York, Nieuwenhuis will be used as a defensive replacement to Lucas Duda in left field, and Valdespin will be used strictly off the bench, "with strategic starts against some right-handers."
Earlier this week, Collins expressed concern about the outfield defense without Nieuwenhuis, so it's not unexpected he made the team. I get the feeling his role will be evolving, and not strictly as a late inning replacement to Duda. A lot will depend on how Byrd and Cowgill fare against right-handed pitching - if they struggle, Nieuwenhuis might get more opportunities in those situations.
Valdespin is an interesting case. I have to assume Collins is still not sold on Valdespin's outfield play, which is why a) there is no platoon out there, and b) he didn't win an outfield job outright. He did have a strong spring, but so did the guys who won jobs, and all of them are either outfielders by trade or have more experience than Valdespin. The question is, will the strong camps for the three starters carry over and be sustainable? If it does, that answers a major question about the outfield. If it doesn't that's where Valdespin could fit in.