There's one bug I know was in 31.25 that only dfhack helped you with -- buckets that would get a mix of water and something else (lye, usually) in them and become both unusable -- and unemptyable, hence unable to be made usable again... dfhack had a fix for that. Pretty much the only place I would want to use it because 1) while hacking, it's not cheating so much as fixing a bug and 2) I couldn't do it without dfhack (all the other legit uses, I'll just take the time to do myself).
That said, I don't think you're a cheater if you use it just to work around some of the weirder quircks of the game or something. If you used it, on the other hand, to do the RTS equivalent of powerlevelling except violating the game mechanics rather than exploiting them, that's cheating. If you do it to automate something that you could do yourself (which I guess it technically more like powerlevelling), it may be the cheap way to play the game without being cheating.
That's a concept I think a lot of people lack -- it doesn't have to be either bigtime cheating or perfectly standard, it can be stuff in between. Cheap shortcuts and third-party bugfixes are just a couple examples. Then there's mods -- taking one game and making it into something else. That simply defies the framework in which "cheating" exists: if you redesign the rules in any way to suit some whole remake, that's different from breaking the rules in the original game. Of course, if you're playing a mod you're not really playing Dwarf Fortress strictly speaking -- but that's exactly why it's not cheating, because you can't cheat at a game you're not playing.
On another wild note, I've heard of a couple handy utilities that utilize dfhack. Example: if I'm not mistaken dfhack is required for Dwarf Therapist, which (generally) doesn't do anything you can't do in game, but puts all your data and options in one place for ease. Another example: various 3d visualizers have, historically, connected through dfhack. (However, I believe the most up-to-date one, Overseer, is about to get a remake that will use the map data in the save folder or maybe some sort of export. I _think_ that implies it won't rely on dfhack.
If the elves here were like Tolkien's I'd say I'm one of them -- "Do not go to elves for counsel, for they will answer 'Yes' and 'No.'" However, we all know elves are a mysterious hybrid of hippie businessmen who want you to only buy trees from their inexplicably friendly log-producing corporations, which seems like a misapplication of the notion if you ask me.