I am new to vamps in game, never really played one, so questions arise.

I have this mod, that allows YA to spawn on community lots, just like any other sims. (YA Visitors Outside Uni )
But it does not say..if it sees, or understand, that my YA is a vampire..or not.
Visiting a community lot during the day, you have 0 chance to see Contessa showing up...she might show up at sun down though, but never before.
For those of you who might also have this hack..can you tell me if there is a chance while playing another household in my main 'Hood, that I'll see my YA vamp browsing for clothes in daylight?

I would hate witnessing his death, while I cannot play him...

Any Sim that is designated a vampire will not spawn on community lots unless it's between 7PM and 7AM, whether they're the NPC "grand" vampires or a playable one. I'm pretty sure it's hard-coded into the game, so no worries. The only way you could get a vampire on a community lot during the day is if you send a playable one there yourself.

That said, I have had some of my playable vamps brought home by other playables as a "friend from work" during daylight hours. When that happens, the vamp runs off the lot and a little message that says something like, "ARGH! The sun! I must flee!" pops up in the corner of the screen.

Good. Not let's just hope that mod I have, does not break this.

It shouldn't. It's not broken in my game, and I have the same mod. In fact, I have a few extra vamp mods. Like I said, I think it's hard-coded in the game, to protect the vamps. Too bad the coding isn't so good that they don't decide to wander off for a swim in the middle of the day on their home lot. :P