What we've got here is a false sylogism. A false sylogism about Jesus and Santa that is, not about Libertine and Yoko though we could do one of those too if anybody wants. Anyhow, the Belief in Jesus dose not necessitate belief in Santa for the simple reason that there is no necessary connection between the two. The fact that there are certain similarites is irrelevant. You might as well say that belief in Krishna necessitates belief in Santa as the similarites between the two are roughly the same as the similatites between Santa and Jesus. Or you take it further and say that belief in one necessitates belief in the other two. The Raelians believe in a space alien saviour similar in many ways to Jesus, Santa, and Krishna. We don't even need any of these characters to have the same retarded problem. How about this one. The cult of personality surrounding Joseph Stalin during his time in power painted him as a benevolent father figure, same with Hitler, Mao, Pol Pot, etc. . . So, do you like your father? Was/is he kind, benevolent, etc. If so then you must like Stalin, Hitler, Mao, and all of these creeps too. Same false sylogism, different principles.
Santa comes largely from germanic pagan myths, so you can believe in santa and not jesus. But i see what they are saying, would be no different if you replaced jesus or santa with the tooth fairy or easter bunny.