File off the occasional D&D-specific IP (like, say, Tiamat - I think there was quite a bit, but "Orc", "Goblin", "Acrobat" and "Ranger", frex, aren't exactly trademark terms) and I don't think you would do a lot of damage to the cartoon...At what point is something "D&D in Name Only"?
Well, I think that's a difficult question. What you are essentially asking is, "What is D&D?" And as we know, that doesn't have any one answer. And in particular, you aren't making the easier assertion - that the adaptation is unfaithful to a particular story or intellectual property - because when you make something that is just "D&D" as opposed to "Return to the Tomb of Horrors" or "Chronicles of the Dragonlance", it's not clear exactly what you are adapting. D&D is an interactive story medium; a movie, book, or cartoon is a non-interactive story medium. The only thing the two share is the story, and so if you don't have a story to share how would you know that something was done right or done wrong?
Sometimes the core story of D&D has been described as, "Kicking down doors, killing things, and taking their stuff." But first, is that the core story of D&D or the core story of a D&D parody like Munchkin? And secondly, is that really the core story of D&D or just the core story of a certain sort of D&D that mostly does exist as a sort of self-parody in the same way that having the first episode being killing rats in the basement is a 4th wall breaking wink at the audience? And thirdly, and most importantly for my purposes, if that really was the core story of D&D then that would be further reason that the cartoon damns the game and not the other way around.
I don't think that TSR saw the D&D name as boosting the cartoon as much as the other way around. In many ways, D&D was rolling out the same model of business that at the same time was being rolled out (more successfully it would turn out) by GI Joe and Transformers. The fact that Diana was an Acrobat, Bobby a Barbarian, and Eric a Cavalier was deliberate product placement for D&D's new product 'Unearthed Arcana'. The fact that the cartoon had cameos by proto-iconics like Strongheart the Paladin, Warduke the Fighter, and Kelek the wizard who in turn were part of an action figure line meant that the cartoon was supposed to boost interest in toys, which in TSR's case was supposed to lead kids from playing make-believe with the toys toward playing make-believe in the formal structured way of an RPG. On the whole, this strategy was I think well thought out - or would have been had someone raised their hand in a meeting and said, "Since we are rolling out a fantasy product to an audience of children, we probably shouldn't be calling our villains 'demons' or otherwise associating ourselves with any real world occult in any fashion. The last thing we want to do in a story filled with wizards and magic, is give the impression that we are connected with any real world beliefs about magic. It will probably freak some people out, and then the fact that the game that is ultimately driving our RP is adult oriented, often horrific, and built around violence is probably going to concern people in a way it wouldn't if didn't look like we were thumbing our nose at people."
But was it D&D? Yes, I think it was. It had bullywogs, lizardfolk, Tiamat, wizards, thieves, fighters, acrobats, gnomes, orcs, nightmares, shadow demons, cavaliers, barbarians, rangers, halflings, gold dragons, rocs, red dragons, unicorns that could teleport (as a plot point, no less!), illusionists, psionics, shambling mounds, dwarfs, skeleton warriors, giant eagles, hook horrors, frost giants, behirs and most everything more or less has to sort of role that it would have in Dungeons and Dragons except for the 'Dungeon Master'. But the DM being embodied and in game isn't a bad conceit as far as it goes, and helps capture the feel of being in game where there is a DM sitting there with you. There is a party, and they have a quest, go on adventures, fight monsters, solve riddles, and often end up heroes.
Sure, you could file off the serial numbers and the story wouldn't suffer, but do you honestly feel that hook horrors are going to even appear in the cartoon if it's not inspired by D&D?
Maybe even more to the point, in many ways, the cartoon was more grown up and mature than what most people were doing at the time. Heck, I would be happy if I had characters as consistently well drawn in my games as the kids. Just as the introduction of less paragon Superheroes with ordinary problems and relatable normal drama was seen as an evolutionary (or even revolutionary) step forward in writing quality in comic books, so the fact that the kids weren't just brutes kicking down doors, killing things, and taking their stuff but kids with real world problems, understandable fears, and relatable emotions was I think a step in the right direction.
Let me ask you this: when has there ever been anything faithful to the in game story of D&D in its ideal? The best D&D movie by far is 'The Gamers 2: Dorkness Rising', but that movie isn't faithful to D&D so much as it is faithful to the act of playing D&D. The in game story is a parody because in real life, the in game stories we tell in transcription so rarely even rise to the level of good parody. The same would be true of the D&D episode of 'The Community' which likewise isn't about D&D so much as it is about playing D&D.
If this isn't D&D, what would pass your test?