This is such an open question that it's hard to pin down a consistent, concrete, and cleanly delineated answer. If you get one superstar player out of a draft and nothing else of value, does it make it automatically successful? Does it matter if that player was taken out of the 1st round or the 6th? Does it matter if you hit on that 1 star in a draft where you had 8 picks vs one where you had just 5? What if you trade every single pick in your draft but one, but that one pick made ends up being great? Is it a great draft because you batted 1.000 in a small sample size? Or do you question the returns on those trades, especially if it was considered a strong draft and you might've gotten more good players from it?
Is there a set # of players that makes a draft successful? Is it 3? If you get players to each play 500 games in the NHL, is it a good draft? What if all 3 of those players are depth guys (4th liners, bottom-pairing D, a platoon or backup goalie who gets 15-20 games a year)?
What if I told you you could have a draft where you'll hit on 4 of your 10 picks for a total of 1,200 games? That sounds successful by some standards. But what if that draft was Columbus' 2003 draft where they got Nikita Zherdev, Dan Fristche, Philippe Dupuis, and Marc Methot? Now it seems kind of awful that in a draft of historic reverence they got the biggest 1st round bust not named Hugh Jessiman a pair of forgettable role players, and a guy whose biggest NHL contributions have come in another uniform.
The Sharks in
1998 got over 2000 NHL games from their draft. Is it important that almost half of those were from Marco Sturm, and the other half came from the largely-considered-disappointing Andrei Zyuzin at #2 and good depth guy Matt Bradley in round 4 (who accumulated the largest majority of his games in the NHL outside of a Sharks sweater)
What about using picks or prospects as trade chips? Does trading Setoguchi in the Burns package redeem his value a little bit? Does Charlie Coyle become a "good" pick for the Sharks value-wise because his primary value for the team was in that trade (simply becuase he didn't have time to build up any in-organization value contributions)?
I realize this seems like kind of a weasely non-answer, but I feel that there are too many moving parts in a draft and outcomes to be able to set hard criteria on what does and doesn't count as a "successful" draft based on simple thresholds like "X games played from at least Y players or Z% of players selected"
A successful draft kind of seems like that famous quote about pornography: I don't know what it is, but I'll know it when I see it.