I was looking through the requested games, when I noticed that some of the requests are repeats, while others weren't on PC in the first place. For example, games like "Haol 3" shouldn't be on the list. Is there a way to flag these types of games?

No, the wish list is not being officially supported anymore and even when it was duplicate entries where left untouched just the same.
The wish list doesn't have any real purpose either because at first GOG needed to know which games the community wanted in general but a higher number of votes never equaled a higher chance of getting the game here. I think right now GOG already knows which games people want so they don't bother advertising the wish list anymore.

I would rather just restart the wishlist somewhere else so that it would have some actual support, just for our own fun since GOG doesn't use it.

We've been asking for that ability for well over two years now. If and when GOG does finally "reboot" the wishlist as they have said they will do, we might get that ability, but as it is now, the wishlist is only useful for keeping "want this game nao!" threads off the forums.