For many years my tube was part of my bass boat. When not fishing a tournament, I often hop in the tube and get back into the spots I can't get to in the boat. Most of my fishing is in Texas, louisiana and Mississippi. Gators are common in all of these states. I never had a problem with a gator, I have "been wise" several times a got out of the water when I encountered a 8-10 foot gator. You never know what they may do. snakes are a different story. I have worn out several good flipping (dabbling) rods beating snakes off. I have had them try to get in the tube with me. Have pulled up the stringer to add a fish and found a big old snake hanging on to one that was on the stringer. (thats why most tube fishermen use baskets, but heck, they get hung up in the brush and restrict your movement.)
Piece of advice. If you do much tube fishing is snake/gator country, then find a good friend to fish with. Look out for each other's back and try to stay close together. As an added bit of security, drill a hole in a long broom handle, tie a stout cord to it and let it float along behind you. It's great for beating snakes. Of course, if its legal, a .22 with rat shot is great too.
I don't do much tube fishing anymore, but I still have some fond memories.