Yeah, it's better to be safe. It would absolutely suck to find out someone else was profiting from your hard work >.< I'd be pretty devastated if it happened to me, so absolutely appreciate any heads up :3
That sucks that it's something that happened often with Steam Greenlight >.<
It's not quite the same thing, but I've occasionally come across commercial games on Steam where I recognise the sprite assets because they're ones I've downloaded myself, and realised, hang on a minute... the terms of use for those assets state that they're for personal/free use only, and commercial use is prohibited >.< I'm guessing the devs think that because the assets are from Japanese artists, they'll never find out, so they can do whatever they like.
The first time this happened, I contacted Steam about it, but they weren't interested in what I had to say, even though I provided direct links to the assets and their terms of use >.< So I just gave up!
Hope you have a brilliant day too :3