I haven't heard of the personal name TANITH. The Hebrew word for "snake" is "nakhash", and "tan" (tav-nun) means "jackal". "Tanin" is a sort of crocodile, so this is the closest I can get to "serpent" in Hebrew. I have no idea about Egyptian, but I there know there has been some influence on Hebrew names from that side. I will go to the library some time from now (it's a 30 km drive) and check the Encyclopedia Judaica.