I have a friend that keeps 2 females and a male together. They have been this way for about 5 years, no problems.... except (lol).. she has to seperate the male for half of the year because he's so darn horny that the females double-clutch if he stays put.
I've heard to keep all males seperate because they might fight...
I know it is usually frowned upon, but I think if they each have a lot of space, fed well and have and good temperments it should be ok.
(hopefully someone with more experience will answer)