I once owned a gerbil while I had rabbits, and made the mistake of putting him (the gerbil) in a box with no lid outside while one of my rabbits ran around. The rabbit approached the box and looked in, and the gerbil lunged up. grabbed the bunny on the cheek, and wouldn't let go. Poor little rabbit, I had to pry the gerbil off of his surprised face. Thankfully he hopped away with nothing more than a small mark and a very bruised ego.
That's the only experience I've ever had with gerbils and rabbits.He was the only gerbil I owned, and he was very aggressive with other animals. I do know that you should never mix species such as gerbils and mice (you will most likely lose someone if you do)...so personally I wouldn't recommend it. However, I did keep my friend's guinea pigs in with my rabbits when I was a teenager and never had problems with them. I think the smaller rodents though, such as mice, rats, gerbils, hampsters, etc., should not be intermixed.
