Cooking with rattlesnake is truly an unique menu maker.
Rattlesnake meat is a southwestern delicacy. If you haven't ever eaten rattlesnake, you are in for a real treat. No, it doesn't taste like chicken! It has a much gamier flavor, much more reminiscent of pheasant, frog legs, alligator, or even elk. - Cooking with Delicious Rattlesnake Meat
There are some out there that say rattlesnake meat tastes like chicken. Never having tasted rattlesnake meat, I cannot make a recommendation by personal experience. There was a restaurant here in town that once served python. I never tried it either, but they recommended having it with wine. The restaurant has moved on so I cannot say which wine they actually recommended.
That said I will go out on a limb and suggest a Shiraz or Chianti. I will use this as a suggestion:
Wild duck, goose, partridge and pheasant meat is very aromatic and is paired with stronger, aromatic wines in comparison with the wines paired with domestic poultry. Choice of wine depends on the age of the bird and its preparation.
Young roasted partridge or a pheasant has a less intense flavor compared to older birds so light red wine such as Shiraz or Chianti would be appropriate. If the meat is prepared with thyme, then a more mature red Burgundy would be more appropriate. - Learn about wild game wine pairings