Christmas started, I believe, in the 2nd or 3rd century. If anyone for those beginnings saw what it is like today around the world they wouldn't recognize it at all and it's only been 18 or 19 centuries and on one planet. Now draw that out to 30 more centuries and 11,000 worlds with the infusion of other non terran races and cultures and environments. I'm not saying the holiday can't exist, not at all. If we follow our own history, we would not recognize it either BUT we may recognized certain elements that influence local or regional interpretations.
HOWEVER, this is Traveller and anything in this huge empire is possible simply by the odds. The best image is a world colonized in the early days of Terra expansion by people who were really into Christmas as we know it today in certain locations dependent on the Earth region or culture of the colonists. They settled and aimed to celebrate all the trappings of the holiday.... religiously. They may have chosen or found a world with a cooler climate so white Christmases in that world's winter are the norm. They may have brought evergreens of many types and reindeer livestock and any other trapping they see as the holiday season. Rules and laws could keep Christmas in your heart all the year for the habitants almost like Whoville so it endures all those centuries.
Now, the novelty of this could be attractive to travelers from other worlds. It could be a basis of the economy and speading it beyond if only as something fun and exotic. It may catch on here and there. It could spread the religion in what form exists.
I can see people carrying various decorations and such on their ships as good luck trinkets or a reminder of something good and beautiful and bright inside cramped hulls of metal in seas of vacuum and jump chaos. The original christmas day could become vague and become attached to local seasons or established holidays so they can focus on bringing out the crate in the hold and brightening the ship for a while with shiny baubles, artificial evergreen and statues of Santa and people having fun all to remember again what Christmas is all about.
Oh yeah, it can happen.