I find annoyance at someone for hacking your work to be the height of hypocrisy. If you feel that way, then you probably shouldn't be hacking at all. I don't condone theft of another's work; however, seeing how it works is perfectly acceptable. I don't think curiosity should be curbed, especially since it is the foundation of the entire community.
Except, remember what this even is -
ROM hacking. Some people may not explicitly thank or give credit to Game Freak, but there's always the implicit credit simply by virtue of their game being a ROM Hack. Ultimately, it's obvious that not all of the work is entirely their own, and it's easy to tell what mechanics they changed simply by being familiar with the original.
Compare that to taking a ROM Hack and essentially using it as a ROM Base. Maybe there's a hack that adds new Pokemon, items, moves, and the Fairy-type. You take it and build your Hack overtop that without explicitly crediting them. In this situation, it wouldn't be even slightly obvious that those weren't your own work.
Pretty much the only situation that it would be obvious is if you just made a couple of small changes and tried to pass it off as your own.
However, all of that is only if someone doesn't give credit. If they do, I'm perfectly fine with it. If the original hacker explicitly forbids using their hack, or they specifically ask you to stop or take down your hack, I think you probably should, just as a courtesy.