Actually, wolfdogs can exist naturally. This is especially seen in Europe (hey, Eurasian?!) and usually only occurs under very specific conditions, hence natural wolfdogs are extremely rare (sources:
https://www.thelocal.de/20180620/could- ... se-dangers &
https://www.zmescience.com/ecology/anim ... -82462433/
"Despite the evidence of widespread hybridization between Eurasian grey wolves and dogs, the team notes, wolves have remained genetically distinct from dogs. This suggests that cross-breeding with dogs isn’t enough to blend the lines between the two species, provided it occurs at relatively low levels."
(The latter source referencing tours ancient dog DNA)
The most common scenario is when a dispersal wolf encounters a stray dog. Dispersal wolves have left their natal pack to start a family, and if a wolf happens to come across a dog then they will seize that opportunity, as they aren't territorial (because they have no territory) and basically see dogs through "rose-colored glasses" during breeding season. Wolfdogs can definitely 'join' packs, or at least be born into one with recent ancestry. It's not impossible, and it has most likely already occurred in Yellowstone from my very own observation (high content wolfdog). Check out this post
viewtopic.php?f=6&t=88488
Depending upon the content, a high content wolfdog would likely have success in the wild, as they can be nearly indistinguishable from pure wolves both mentally and physically. Mid to low contents, however, are another story. They would most likely not be able to compete against their larger, purer cousins without sticking to human settlements.
Wolfdogs in the wild can be more dangerous than captive bred ones. With captive breds, they are usually socialized and associate people with something positive (enclosures are also a huge part of it). As we've seen in the past, Wild wolves who become habituated to human presence by themselves are risky (e.g. will kill pets, get close to people, raid trash cans, kill livestock) and will eventually be shot. (Source:
https://www.nationalparkstraveler.org/2 ... uated-wolf). Now imagine a habituated wolf with 3x the prowess. That's a wolfdog.
You're correct about unrelated wolves occasionally joining larger packs. Junction Butte for instance has about 3-4 breeding females and has surpassed or almost surpassed the druids & are about to break the largest wolf pack record. (Source:
https://www.yellowstonewolf.org/yellows ... ?pack_id=3). However, it's far more likely for a wolfdog to
start a pack with a dispersal wolf instead. Large wolf packs with 30+ individuals are exceptionally rare. Anything beyond 30 something wolves is sort of breaking your realistic social dynamic theme.
TL;DR
To end my rambling, it's not unrealistic, but I would say it's unlikely and it's cool to add flavor to your story. However, if you really want to be as realistic as possible (minus the magic), opt for another wolf instead.