Just checked and yes, it seems it is.Isn't the flying snake also their symbol now?
In the great upheaval for Storm Kings Thunder there is a Zhent that has a flying snake as a familiar or pet.
I didn't see a challenge rating requirement for the find familiar spell.
bat, cat, crab, frog (toad), hawk, lizard, octopus, owl, poisonous snake, fish (quipper), rat, raven, sea horse, spider, or weasel.