Santa's Summer House is the saga of some low budget Californian "film makers" that had use of a house large enough to set up cameras in and apparently couldn't get the permits straight to do porn, so went with stuff like this instead.
As best as I can tell, a group of people who may or not have known each other previously are in a shuttle van in route to a resort hotel, and the van gets lost. They end up asking for directions ... I guess at a house where Santa Clause stays when it is not the holiday season, and pretends to be a regular person. They gradually discover hints that reveals the man's identity. I think if I remember, Cynthia Rothrock produces a business card that says "MRS. Clause" on it, which is a hint right there.
Its supposed to be like a Hallmark type of movie where this is all part of a secret plan Santa has to help the visitors be better people or something. Somehow, finding the hotel they were supposed to go to is impossibly difficult for ... reasons, and Ms. Clause offers to let them all stay as guests. Everyone except the guy that was driving the van shuttle. He just kind of fades out of the movie. He abandons the people and returns to his point of origin, or he just got wished to the corn field or something. It doesn't matter. This is where it is seen that they made some writing adjustments so Rothrock could be a more load bearing component of the narrative due to relative acting ability. She has a lot of lines; more than anyone else including the titular character, and I suspect this was due to her being the most able of the cast to memorize lines. She says a lot of "my husband says..." lines in scenes where the Secret Santa don't got enough people, and is not in the scenes. Anyway, Santa comes into play eventually, and there is a whole thing where someone accuses him of being Santa very early on, but later when he confesses to being Santa he is not believed, but then he knows things about them and has some of their childhood letters to Santa, and it is obviously the same house as the talking cat movie, and is an obvious low budget cash grab and the whole thing is just a mess.
What is kind of baffling is the dog being the centerpiece of the cover art. The dog is barely in this movie. The dog is not magical, the dog doesn't do anything, the dog is barely spoke of, and the dog doesn't wear a scarf. There is just a small dog that hangs out in the background sometimes. I don't think it was mentioned or even implied that the dog was a reindeer taking another form or anything like that, and neither is a small dog any part of Santa legend. I suppose if you just must experience Santa's Summer House for yourself, go ahead and watch the Rifftrax version, that has to inevitably make it easier to get through, and you are probably watching the movie for meme value anyway. I guess another possible audience is, those kinds of very repressed families that are overly careful about only watching "wholesome" content and got tricked into somehow paying money to see this. It seems like that is the target audience. Considering how much of this type of thing exists, there has to be a market somewhere. It is hard to imagine someone going into this unironically, but it must happen. I would guess it is what super Christian families watch as something "neutral" without a direct Christianity reference or plot. Maybe they have groups that deem how "safe" secular films are, and movies like this rocket to the top of the list for being non-violent and non-threatening, and not having Scientologists involved in the production. This is all just speculation though.