I think that almost all of "special" AI structures can spawn for any AI type, not just the AI type that loves to use them.
Like, I have seen captured settlements on non-entrenched homeworlder AIs.
It's just that the chance to encounter them on an AI type that doesn't specialize in them is very, very low.
So seeing 1 or 2 Neinzul viral swarmers is not always a sign that you are fighting a Neinzul viral enthusiast. If you see more than 2, then you should start strongly suspecting it.
One exception to the special AI structures is the "Cloak everything on the planet" structure, which I think has 0 chance to spawn unless the AI is the Shadow Master.
However, such structures are the exception, not the rule, AFIAK.