It depends where you "release" them as townies.
Thus, townies you create and release downtown will become downtownies and likewise for uni (ya only, of course) and your main hub.
I don't think that's true at all. Townies don't specifically live ANYWHERE as such. They are simply folk who wander the Neighborhood. Furthermore, they stroll around from one SUB-Neighborhood to another, so there's no such thing as Townies versus Downtownies. Not as far as I can tell.
YAs at Uni will visit both Residential AND Community Lots in your Core 'Hood and your Downtowns(I've seen them there). And, prior to Installing the "No Shove After Look Through" Mod, I found that one of the Dads living in my Core Neighborhood had a habit of turning up on Campus to do the shoving.
It is however true that Uni NPCs, such as Cheerleaders, Streakers and Mascots etc. will only do their annoying BS On Campus, although there's a hack on MTS2 for people weird enough to WANT these irritating NPCs visiting their NON-Uni 'Hoods.
But, apart from the Uni NPCs, which I always BAN from all my Lots, thanks to Twojeffs' marvelous work, I don't honestly think it matters WHERE you make a Townie or NPC. I THINK they'll show up just about anywhere.
Though I haven't looked at the coding, so I couldn't swear to it.