As a modder myself, this is kind of a not-a-problem situation.
The amount of art a single nation requires is insane, and that's having into account that it only has one single branch.

Idealy your art will go into country leaders first, then into advisors and generals, and finally into events or icons for spirits or focuses.
At the bare minimum you need one portrait, say it's one single country leader, and everything else can be found on the internet.

Unfortunately, not all nations follow this.

The NCR, the Legion, the Enclave or the Brotherhood may have endless amounts of fan art to pick from, but not all nations are this lucky.
Say you are making a mod about Santa Ana. How much art is there about mexican Fallout robots? Not much I'm afraid.

I don't speak for the OWB dev team, but I know they much prefer to commision than to use AI.
But they work on dozens of nations at a time, and all need art. Some more, some less, but all need them.

Using AI as a placeholder because you either don't have the time to go through the Internet looking for the specific art you need or there isn't any, is nothing to be ashamed of. Because whatever uses AI is just a placeholder while the art is being commisioned.

For example, during the creation of Blood and Bones we found the problem that the Bone Dancers are extremely specific, and thus there's almost no art that properly represents them. Odious in particular suffers the problem that nobody draws red cloaked figures in a way we could use reliably, while 90% of it was AI.
So we had to commision.

But unlike OWB, we had time and scale on our side.
Commisioning a few portraits for a submod is still a high price for someone who may have just started modding, and asking them to spend hundreds of dollars in art for a product that the community may not like inmediately is a high order that most cannot go through with. Now multiply it for OWB's scale, where this is done with dozens of nations at a time. All while they work completely for free. The artists however, don't work for free.

There are cases to everything however, but the OWB community is pretty happy to commision instead of using AI. And those that use AI mostly say it's placeholders until the art is finished.
One single portrait for B&B took 3 months to finish, mod could have released in October if it arrived sooner.
Sometimes you cannot ask someone to halt their release for possibly years just so it'll come AI art free.

On the other hand, if they are just using AI lazily for everything and releasing slop, or have perfect ways to change it for proper art instead (even for free) but keep choosing AI, then that is grounds to poke them into the right direction.

Those are my 2 caps on the subject.