As to reasons to name a hound Rattler, adding to Janey's above:

4. He's a rattling good hound. ("Rattling" is an intensifier in the south as in some other places. This is a rattling good thread. Hope my answer is a rattling good answer.)

5. Some dogs are adept at killing rattlesnakes -- this was what I always assumed was the origin of the name in Grandpa Jones's song ... he was such a good hound he'd even kill you a rattler and never turn a hair.

OK, now I'm rattled.

Bob