You are wise to be afraid. Last year, HG pulled two games which used AI art.
If you don’t have the budget for it, stock images and some editing should be enough. Plenty of HG authors do that. Bad cover art could damage impressions of your game, but there’s probably limited benefit to going from good to fantastic cover art.
(Granted, one game is a serious eyesore in my library because of lazy image scaling.)
I mean, I did this for someone else’s game. It was free. If you seriously need help with the art, ask around.
Legally, as long as you have a license (does not have to be exclusive) to use the art commercially, it is fine. Look for CC0 images or content on Pixabay.
I don’t think there’s much value add to doing so. Plus, I think some writers who added it ran into some technical problem or another, so… probably not the best.