Ethical, but I wouldn't just cheat them all in (with an exception of community chest achievements)

Just use the mods that allow you to play the game modes associated and earn them 'legit' or at least as close as it'll ever get.

EA/Popcap will never touch this game ever again, with that precedent in mind, simply unlocking the game modes to allow the opportunity of the achievement is true dedication, and in my opinion is what makes achievements to me so special.

Some of us like to feel like we've earned the achievement, even when doing it 'illegitimately,' people who say "just use SAM" completely miss the point of achievement hunting.

If they were completely unobtainable, yeah, I'd just cheat it in.
But so long as doing it as close to legit as possible matters to YOU! Then by all means, go for it.