So, according to UESP, the Traveler is a vampire who can appear anywhere, and attacks you on sight. Apparently, he's the only way to get a set of Vampire Gauntlets without having to start the Dawnguard questline. Does anyone have any information on him, especially how to find him? Because I want a set of Vampire Guantlets, but don't feel like working my way through the entire Dawnguard questline just to get them (I generally side with the Dawnguard).

You'll find him

I found him just outside of Ivarstead.

I am not sure, but I do not think you will even see him unless you start the Dawnguard questline, my main character had an exceptional rate of attacks before joining up, but that one he never got, even after he joined he never got a Traveler despite still getting attacks, he joined the vampires. The second character only got a few paltry attacks out in the wild before joining up (Dawnguard) killed lots of Travelers had lots of town attacks the third character is not up to such creatures.

I wish you luck with your search anyway, but he is just a random event so no way to say where you will meet him, just keep ignoring the hints to join up and he might eventually turn up.

It is not necessary to go through the entire quest line to get the gauntlets, its a random encounter so there is nothing you can do to specifically trigger it besides play a lot and travel around.

Is this "Traveller" in the vanilla game or must I activate Dawnguard to have it?

You have to have Dawnguard.

My character actually encountered him twice so he's probably not unique, first time in Ivarstead and second time in Rorikstead.

But Traveler isn't the only NPC that wears vampire gloves, you can get them from NPC 'Visiting Advisor' that is part of a radiant quest for DG. This information is missing on the UESP.

I always found him at night in Whiterun. He spawned between War Maidens and Breezehome.

First and only time I saw this "traveler" was in Riverwood. I saw a robed and hooded individual heading towards the sawmill. I accosted him, and he attacked. He had on some hooded black robes and the vamp gauntlets.

Never seen that guy and I've played Dawnguard...

You don't need to actually play any Dawnguard quests in order to see its random encounters, as long as it's installed and you're lvl 10 or above.

The thing is, I'm not looking for Vampire Gloves; I'm looking for Vampire Gauntlets. They're the Light Armor version that apparently almost nobody wears.

Anyway, it seems that I have to at least start the Dawnguard questline to get the random Traveler attacks. Does anyone know how far in I have to go?

Yes, I know that, but I've never seen him, anyway.