Season's greetings! I think the Empire would be heavily integrating Christmas and New Year into its festivities ever since the migration to Nueva Castile
Definitely
Plus we should assume that there are Empire-wide holidays and local planetary ones
New Year, Great Father's birthday, Establishment of Imperio, Victory Day in Amaris War, Star League founding, etc... would be celebrated everywhere
Then we have Christmas, Easter (both calendars), Eid al-Fitr, Hanukkah, Colony Founding Day, etc... which would be celebrated depending on the planet and which folks live there
It's quite possible that big local events like, for example, the date when first Castilian colonists arrived in the cluster would become Empire-wide holidays as well due to historic significance
Plus I'm sure that even back in the Homeworlds Clan civilians celebrated all sorts of holidays once they were off the clock and back home, Scorpions have well established tradition of warriors and civilians not tripping over each other too much
Now in the Empire it would be even jollier