Herb Ox,
Sorry if this response comes in late...better late than never, eh? =)

Ill try to keep it short and spare you the Herpetological details of the discussion. The short(est) and sweet(est) I can do:

Generally speaking, theres are 2 glaring traditional factors I can think of that one would use a snake (any snake) in wine:
- They shed; from traditional perspective, this can be seen as having an ability to regenerate the exterior quickly.
- Flexibility; no doubt seen as a method of controlling, tightness and things like arthritis in the body.
- There are other factors but these things are less important, IMO.

A bit more specific:
- A third one springs out for venomous varieties, and that is of venom of course: Venom has many many medicinal uses; relieve convulsions, anticoagulant, relaxant properties, channel opening, etc etc etc. The lsit goes on and on and whole lives of work are done on venom.

Most Specific:
- Cobras are elapids, which is the same family as that of the commonly accepted Bai Hua She (I say commonly accepted because while the presently used bai hua she species is a Krait, most people actually know it as a Viper, which is NOT what is presently used and accepted as of today). So while there are some obvious reasons right there for using a cobra in wine, it is kind of odd because Cobra venom is not particularly potent. Perhaps it was simply easier for them to obtain a Cobra than a Bungarus Krait?

Lastly, are you sure it was a cobra, and not just a false cobra, or a rat or hog-nosed snake, or a number of other snakes that mimic cobras as one form of natural defense?

Regardless, interesting story, thanks for sharing!