Personally, I wouldn't house a rabbit and a guinea pig together. Rabbits have incredibly strong back legs and although they may not mean to harm a piggy, it is easy for them to do so.

However, in the past I have had a rabbit and piggy together, but they were introduced when they were both babies and bonded well. Sadly my piggy had to be put to sleep at a young age, but the bunny could well have caused an injury as she would have been twice the size of the piggy.

What do other PT's think?