No, not in any uncertain terms. Ron Gilbert could work in espionage as his secret-keeping skills are first rate. I'm sure you must realize that explaining the ending to Monkey Island 2 is a question with as many answers as people who have played the game to the end.
The "cannon" (at least as far as all subsequent Monkey Island games are concerned) ending of Monkey Island 2 explained in Monkey Island 3 states that
it was a hallucination.
but the designers of MI3 had no insight into the original intentions of the end of MI2 as Ron Gilbert was not a part of that project and his original intentions were not shared. Because of this, many players have picked at the inconsistencies in the MI3 explanation as you do and consider the explanation provided in MI3 not to be cannon to Ron Gilbert's original vision which he seems intent to never reveal.
Ron Gilbert never explained what the Secret of Monkey Island is either. From the many interviews and ambiguous answers, it is rather clear that Ron Gilbert likes his secrets and may have no intention of ever clearing up any of this conundrum. He mentioned that he considered giving it to his lawyer to be read upon his death, but that this may lead to his untimely demise by a crazed fan desperate to know the secret.
Is any of it real? Is it the fantasy of a boy in an amusement park? What is the secret of Monkey Island?
We may never know. The wikipedia article has some good references and insight, citing several interviews with Ron Gilbert. Apparently Ron Gilbert intended a trilogy so the ending of MI2 may not have been meant to have the finality it almost implies if you take Guybrush's experiences at the end literally.
One stronger theory linked from the wikipedia article suggests that
when LeChuck first curses Guybrush after he falls down the hole, he does transport him to a parallel universe of hell and Guybrush's understanding of the world is shattered.
but it could even be as simple as something like
when falling down the hole or upon the landing, Guybrush hit his head and everything after that was a concussion-induced hallucination.
Any explanation that dismisses Guybrush's experiences at the end as being a hallucination is likely not going to please fans and so that's probably why it's for the better that it stays a secret. The best part of the ending in my opinion is that it is somewhat open-ended and allows players' imaginations to run wild and question the reality within the Monkey Island fiction. It's sort of surreal to be considering the "reality" within a fiction.
Personally, I feel that the scene with Elaine after the end makes it pretty clear what's what, but that's just my personal opinion. Either way, the game is a masterpiece.
I'm not sure if Ron Gilbert is making a joke, but on his blog, it reads in the upper-right link to his twitter feed, "When @grumpygamer gets 1,000,000 followers, I'll make another Monkey Island." If that's true and someone's motivated enough to find out the truth of the Monkey Island mysteries, then it would seem some advertising of his twitter feed would be in order (he has 22478 followers right now, only 977522 to go :P). FYI, Twitter has about 360,000,000+ registered users, of whom about 140,000,000 or so are believed to be active so you don't even need 1% of all twitter users to follow him - easy, right?