I know he fights with one-handed weapons, but does he dual wield?

It depends on what you give him. I've only seen him pick up a second weapon rarely, but if you hand him one he'll sometimes use it.

I think he's a one handed specialist who falls back on destruction magic and archery from range. I don't think he uses dual wield however.

Hmm, I've been thinking about arming him with these fancy big twin daggers called "Tantos" to dual wield. I thought they'd suit him far more than the sword I was considering. But if he doesn't dual wield I think I'll opt for the sword.

Can't say I've ever seen him dual wield but it would be awesome to find out. Maybe I'll try giving him another sword and see what happens?

I'm pretty certain he's a Spellsword. Also kind of on topic, I accidentally made him wait in that one Dwemer ruin that fills with water and forgot about him.... took me an hour to find him...