I don't think it would be fair for me to speculate on what CBS should or shouldn't do, not because it's UBT but because I just don't know enough about the particulars in what CBS wants from the show. My guess is that the people behind the UBT don't really care about ratings as much as they do getting people to participate in their tournaments. And CBS has to weigh the opportunities this show offers them in comparison to other options. So I really can't say what either party should or shouldn't do.
As for Christmas, as I mentioned, it's an odd day ratings-wise and you'll see a lot of flucuation from time period to time period and within the day. But HUT levels (households using television) are higher than usual for that daypart. That affords an opportunity for higher ratings, and gaming shows have been successful counterprogramming to sports, particularly the NFL. Christmas or otherwise, a good ratings story for Blackjack is a win for everyone. Hopefully there will be a lot more blackjack on television in years to come...