Rabbits and guinea pigs in the same cage are a big no. Firstly because even a little netherland dwarf has a very powerful kick, one kick from a scared or angry rabbit could seriously injure a guinea pig.
Secondly different dietary needs, piggies need extra vitamin c, its a been a while since I've owned a rabbit, but I know the food I fed him had added vitamin something and it wasn't vitamin c. So unless you feed them their pellets seperately, which would be a lot of hassle, your pets wouldn't be getting the right nutrients as they would be constantly eating each others foods.
Thirdly, they are a completely different species, piggies communicate with a range of squeaks and other noises, and rabbits communicate largely using body language alot of which is characterised by movement of their large ears, which piggies don't have. Therefore they will not be able to communicate with each other properly and this would probably be very frustrating and stressful for both animals.
Then there the diseases, I don't know what diseases and illnesses rabbits can get, but I do know that some of them can probably be pased to piggies.
So whilst I would say it would be okay to have a couple of rabbits and a couple of guinea pigs in seperate hutches and allow them to interact under supervision during floortime, I would not say its okay to allow them to live together in the same cage/hutch.