Can wikis on weird gloop use their own domain names? I feel like that is the best way to ensure that they can leave and that the host can't keep a zombie version of the wiki that hogs Google search position.
To they can. See the Minecraft wiki for example: https://minecraft.wiki
Currently, every wiki they host is on its own domain (besides the meta one)
From the article
> (hint: it’s all about the domain). If we ever start going down the same path as Fandom, everyone can just leave! I would love to see other wiki platforms start to do this, because I think it’s the only way you really solve the problem.
So yes, the wikis have their own domains for this exact reason.