I have done 40 FFA AI on Big US or other huge maps before. It works fine for me most of the time. A better question is wheter you gain any 'value' from 10 extra AI's. It's mostly a case of "why not" for me.
EDIT: well on the standalone at least it works :P
ex)
https://www.warzone.com/SinglePlayer?TemplateID=1009077https://i.gyazo.com/ec22ed69a061c10cc7094b9138fcdc7b.jpg
Edited 10/16/2018 19:00:57