The reason Wolverine is able to hang with Hulk is due to his power set. The adamantium skeleton and healing factor combined let him soak Hulk's main way of damage (Blunt force), and his claws provide the necessary tools to leave damage on Hulk. Combined with his superior superhuman speed and top tier fighting skill he is able to out maneuver Hulk. This is why Wolverine is game for Hulk. Not saying he beats Savage Hulk or anything like that, but these are the reasons he can keep up with him in a fight.
Summed up nicely.
I even think the wolverine could beat guys like the thing for example.
I agree that Wolverine can take a majority over the Thing. As for Hulk, he can probably take a majority over Grey Hulk and other versions below him, but once you start going to stronger versions of Hulk, then I think he bites off a little more than he can chew.
He savage Hulk is a little out of his league, he'll probably fight for a LOOONG, but hulk has a definitive edge. If thing had a healing factor I think he could survive and possibly beat logan but If wolverine is serious i doubt it.
As for gray hulk, i Agree, though there are a couple of events that make me reconsider their original fight back in davids run.