I notice that the filetable, as well as PJSE Tools OBJD editor both read Happy Holiday and Festive Holiday as base game. I also noticed that the read only value is 139, and that the valid EP flags are set to 0 in the OBJD as we see with any base game objects. Does this mean it is safe to clone Holiday Stuff objects and expect them to be base game compatible? I ask because I'm cloning a table, and the only one I could find that suits my needs is a Holiday table.

You never know for sure until try... Best way is to test it with Any Game Starter

Be careful with AnyGame Starter. It's unsupported, and I had to completely uninstall my base game and all Xpacs, plus I lost all my save games, after it messed up.

Specifically, read the warnings. Lots of people ignore the warnings that it won't work with downloaded games or the later collection packs, only to have to reinstall everything.

...plus, make sure that your firewall / antivirus silently not block it from working,
because if firewall / antivirus will not allow it to copy half of game files
or will not let it to make other important changes, then obviously game may break.

Personaly, i have all EP's installed, use it everyday, reconfigure at least 2 times per week,
and my game has never broke yet.

I cannot use AnyGameStarter because all of my games are from Origin, and AGS was only made for disc games.

Well, I read all the warnings, had no digital downloads, adore Numenor, and it should have worked, but I really think it is tricky on Windows 7, despite the claims that it is Windows 7 compatible. And I am administrator. Don't really know what happened, it was a nightmare. Anyway, Sims99Fanatic can't use it, and needs another solution.

I have a second computer in the household, a laptop with just Sims 2 base game + patch installed, and I use that for testing. I've had good success with changing flags so that an object that was cloned from an Xpac object works in a base game.

One alternative is to post it and allow someone else to test base-game compatibility.

Yes, you have it exactly right. They're base game compatible.