Didn't Data celebrate Diwali aboard the Enterprise D?
There are precedents.
The only complication is that games like WoW and SWG created fictional holidays based on their universes which were far removed from ours (What a coincidence! Life Day is celebrated during Christmastime!). Star Trek is set hundreds of years in our future. They probably couldn't promote a specific religious or even national holiday, so it would probably have to be stuff like the date of Zephram Cochrane's first flight, the birth of the Federation, birthdays of characters, etc.
My opinion? No, if they're connected to real world holidays or thinly-veiled attempts to connect to real world holidays. I don't like it when the other games do it, to be honest. Most seasonal holidays have some connection to a religious observance, and as an agnostic in the southern United States, I spend most of my year trying to get *away* from religious observances.
That said, I also realize that I'm in the minority and won't complain too much if they stick in there.