Firstly is there any reliable way to make this character or the group of 3 vampires spawn as I've yet to see them on either my dawnguard or vampire lord character.

Secondly is this possible at all playing on the vampires side.

The reason I ask is because I'm looking for the vampire hood to go with my armor and want to know if I should just give up now.

I was told that the hood, like Serena's, is for her alone and no way for you to come upon it. At least, that is what I have been told. If you hear, or see differently, let me know.

Dawnguard have a radiant vampire hunting quest. No idea if it's the same, because I haven't gotten the mysterious traveler either.

Ive seen the traveler 3 times. He was wearing hooded black robes. Which is pretty rare because it only appears 2-3 times in non dlc skyrim. No vampire hoods seen yet

The traveler wears unenchanted Black Hooded Robes. Which is rare. But for the actual vampire hood, not to be confused with Serana's which is unobtainable, can be acquired through Dawnguard Radiant Quests.

I obtained this hood by doing side quests for the dawngaurd in which I had to destroy a "visiting advisor" (vampire) that was threatening the jarl of one of the holds, and he had the hood when i searched him/her after i killed it.

I apologize, I forgot about the "visiting advisor."