While neither of you are in the UK, we have a law now here that says an animal has a LEGAL right to be "housed with, or apart from, other animals" and the RSPCA, among other animal welfare organisations, have taken this to mean that rabbits and guinea pigs should NOT be housed together.
It might be a matter of personal choice but unfortunately I've repeatedly seen it time and time again where a rabbit has started to suddenly attack their piggy "friend". I picked up 3 pigs for this very reason last summer.
As I've said before, you wouldn't house a hamster with a chinchilla, a rat with a gerbil or a child with an orang-utan so I just can't understand why people would WANT to force two completely different species with completely different needs to cohabit or "play" together.