Savestates, patches of rom hacks, emulators, rom hacking tools, etc. are all perfectly legal.
Just think of it this way: If it was originally sold or published sometime in the last quarter century, then it's probably copyrighted and illegal to copy without explicit permission from the author or company that created or published it.
Most savestates, rom hacks, emulators, and rom hacking tools come with permission from the author(s) to copy and use them, and some even include source code.
ROM images usually don't come with permission from the author (which is actually a company for most games) for free copying/redistribution and what not. That's why a Chrono Trigger ROM is illegal. Also, dumping the game from a cartridge doesn't make one an author any more than downloading it does.
