I personally do not have that much experience with bunny rabbits :) But according to Dr. Allison Vanderhoof, a very dear veterinary friend of mine and has a rabbit of her own, says that parasites are actually pretty uncommon in rabbits. Rabbits do not have as many issues with parasites like other animals. If you do want to use a preventative you can use Revolution (Selemectin) which is a topical product. Tapeworms can be seen in rabbits, due to fleas and you can use Praziquantel in these cases.
In Oklahoma/Texas and a few of the surrounding states, I recommend that you should keep them on a preventative year round. We just do not get cold enough winters to kill fleas/ticks. Remember, fleas can live inside your house! So, you could have fleas year round. We want to “prevent” ever seeing any fleas/ticks! If you don’t see any on your pet it means that the product is working.