I have done alot of reasearch on this subject and I found out that most all websites say that guinea pigs and rabbits can have play time but they should not be hosued together because,

they have totally different food requirements, the guinea pig will be the underdog and could get injured, guinea pigs like other guinea pig interacting as a cage mate rather then a rabbit, guinea pigs can catch viruses from rabbits by eating there poop or even by there pee.

I wouldent do it.