I don't see a problem with rattlesnake hunting if you are going to eat it or use it in some way (i.e. skins) or if it is a nuisance in the area that its in. If its not for one of those reasons I don't think it should be legal no matter what the animal is though.
Also, here in Tennessee rattlesnakes are protected. They may be plentiful in other states or maybe even other parts of Tennessee but their population has decreased a lot where I live. Back when I was a kid it was normal to see at least 5 rattlesnakes in our yard every summer. I'm 27 now and I haven't seen a rattlesnake in 5 years.