Actually, Zerg is a term that comes from a lot of places. It is commonly used in video games and by gamers to mean a group of something, usually something bad or unwanted. My friend uses it in World of Warcraft to mean the Alliance. Most people use it to mean aliens.
So, no, they didn't steal it from Toy Story. I'm pretty sure the creators of Toy Story did not make up that word.
And the items on Gaia, look how many users ASK to have items from copyrighted games and shows. Gaia can't use those, so they make similiar looking items in order to keep their playerbase happy without compromising copyrights.