I've run the fed.wiki.org farm for three years. I've seen weeds sprout. I've weeded on occasion. I've not been stung but then I don't represent a public institution.
See Federated Wiki on Digital Ocean for a configuration less sensitive to this problem.
# Background
The delayed claim mechanism was conceived of as a way to remove barriers to participation. This attitude was codified as a pattern. See Have Fun First
I've yet to see a serious squatter. I'm hosting about 800 sites. There would have been more except that every few months I remove all sites with zero pages with a perl script.
for (<*>) { rm -r $_` unless `ls -A $_/pages`; }
I find lots of sites where someone has created a page or two and lost interest. They were probably expecting to enter a conversation and found their new wiki a lonely place.
I encouraged one colleague to try making and refactoring large sites by forking content from my original wiki. He has using five or ten site names.
I've never promised any level of service but haven't filled the site with disclaimers either. I understand that a site in a university setting is a different animal.
I use wiki behind a firewall in my company. I did seek approval for using an open source tool as is policy in my company. I also wrote some words to that effect on my self-page there.
There have been many proposals for account administration. Part of the motivation for Persona was to easily limit use to users from a specific email domain. Selective read access is a requirement for some.