I was leaving Fort Dawnguard and as soon as I loaded in a Redguard in steal plate attacked me. He was hard to kill he kept using potions. Is this a new enemy?

No. Random npcs like this were in vanilla. I think they're meant to be other adventurers.

There was a dikeish "Orc" in the same area for me when I first booted up today lol. Just a random npc.

Never seen him before.. He kept Saying "This is what I trained for!" it was a fun fight. Hope to run into more.

LOL.
I just today had one of them and yes they are very fun and exciting battles.
And to confirm they happen in vanilla.
http://www.youtube.com/watch?v=dU-Kuk-7fK8
...I happened to record it.