Don't forget Man-Thing is immensely strong and has also defeated the Hulk, and between Swamp Thing's connection to the swamp and his ability to detect emotions I don't think Wolverine could sneak up on him there. Wolverine's MA and claws aren't going to do much here anyway.
When he is being sucked drowning into the swamp muck Wolverine will eventually know fear and start to burn. When that happens, his healing factor is going to make for a very long and painful experience as his flesh burns, his lungs fill with water and swamp turd, and he can't even scream any more.
In all seriousness, that man-thing is too big for ol wolvi to take. That man-thing would litterally tear him in half. His healing factor would be overloaded. Hell, even a smaller man-thing can do damage to a man. Wolvie would have to start with the smallest man-things first and gradually work his way up to the Giant sized Man-Thing. Just one man's honest opinion.
thats more my point. he can hang with people like hulk, thing, etc, because their strength works against them (they get tangled and suffocates in man-things mass), not because he is in the same strength class as them. Man-Thing vs WWH would have been interesting for this reason, however, manny does lack a strong attack that might finish the fight.