Santa is only around because of Christmas. Christmas is the celebration of Christ's birthday. If one wants to use Santa to symbolize good things like giving and brotherly love, that is certainly their right and is not wrong.
The marraige of Santa as the Symbol of Christmas is my problem. If you want to celebrate Santa day, that is great, but it is not the real reason we celebrate Christmas. That is why I group Santa with any other end of year celebration, but it is not celebrating Christ's birth. The only similarities between Santa and Christ's birth are that he gives presents as God gave Christ and the wiseman, when Christ was 2, brought gifts of gold franincense and myrh.
Additionally, if a child knows Santa is not real, but Santa is still used in the celebration, than that is fine. It goes along with any other fantasy or imaginary play, like Star wars or GI Joe. Making a child believe in this godlike man who doesn't exist and then setting them up for the fall when you break the news that he isn't real, that is where the seeds of distrust get planted, if you are planning on building that relationship with Christ.
All of this is based on the premise that it is my first and most important goal as a father that my children have a real and solid relationship with Jesus Christ. I want to eliminate anything that may make that more difficult. If I am teaching my kids to pray to God as their comforter, healer, and provider, I want that faith to be unwavering. Jesus said that we should be like the "little ones". Their faith is very strong. If after years of fostering the belief, I then have to tell my kids that Santa, the tooth fairy, and the easter bunny are all not real, but I have to tell them that Christ is real. "Listen kids, I know that you may have felt misled when I told you about Santa, but I want to assure you that Christ is real". Why would I want to have that conversation.
If you don't plan on having that conversation, Santa can be lots of fun and instill some principles of giving and kindness.