Guardianship has nothing to do with immigration, maybe counter productive from a visitor status perspective but then offhand I can not think how the situation would arise. No question I can think of.
If you want him to visit then by all means apply and see. Obviously the Airlines are used to dealing with people who have issues, my Mother visited and needed to use a wheelchair.
Ohh just a thought not sure how his condition would impact Travel Insurance, good idea to check.