Is good ol' St Nick an icon of Christianity or secularism? It's worth noting that Jews and Muslims don't get their pictures taken with Santa. It's a Christian custom as everyone knows. Same goes with Christmas lights, etc.
The Catholic Church of Christ is a new humanity reconstituted and thus has its unique culture that is always interfacing with the world in order to show Christ's sovereignty over the cosmos. A culture must be rich and whole and that means that Christian culture is not going to be built on Scripture proof texts alone. Nobody can live that way. We can't violate Scripture, but our lives are not lived on a minute by minute application of biblical proof texts.
The fact that we have a liturgical calendar, traditions, customs (saying God bless you when someone sneezes), architectural structures, symbols, signs (i.e crosses): each point to the reality of Christian culture.
I think Santa Claus is indeed a health custom, as long as he is not allowed to eclipse Christ, which is the case with any saint.