What you said, Doc.
I specified the highlighted sentence in my post, because Cromartie's injury is one common to football, unfortunately, it's considered part of the game, no one is surprised when you say "ACL" anymore. So I'm confident he can come back from that, considering that he ran a 4.4/40 at the combine - while still recovering.
Allen's injury is to a part of the body that isn't common to football injuries; it's also a part that is more prone to having problems getting enough blood after an injury of any type to it. When the problem is bad enough, the joint itself can become necrotic because it is starved for blood...and if that happens, it's joint replacement and goodbye football. No doctor would ever sign off on someone playing pro football with an artificial hip.
That's not to say that Allen's condition is that bad, or even close; it's to say that everyone comes back from ACL reconstruction, but hip problems are trickier...and if he does have a degenerative condition there, it will limit his career, and therefore his value to the team.
And that's part of my point: that in a draft in which you only have 3 picks in the first 6 rounds, it's ill-conceived to pick a player with such question marks, when other players who fit your description of what you want are available at the same spot.
My point isn't that Allen is bad, or that he will necessarily have hip problems; my point is that if the question exists, and he's a player who's undersized for the position to begin with, (and he is) and other payers are available that fit your need - then you draft one of the other players.
You don't gamble with a limited asset like a draft pick in a talent-rich draft like this one, where you have so few picks to begin with - that's like walking into a casino with your rent money. There are risks you just don't take when you can't afford to lose.