How do I activate them, (so I can upgrade my Wraiths to them) and use HG Wraiths online?

I dont even know if you can...

Let me check.

Yeah, I had a post up about this as well. Apparently this can only be activated in campaign(which is useless since you don't use Covenant) and Skirmishes. They are activated from the Skulls option in the pause menu. There seems to be no way to activated these during online play at the moment which is really lame.

i dont agree with that if u go to FAQ section of this site it clearly says they can be used online....although idk if any one has figured out how to use them yet although i played a game 2 days ago and we rushed by flaming hogs!!

Honor Guard Wraiths are no more powerful than normal wraiths, they just have the fancy gold trim. You can select them under the skulls menu.

In the FAQs it says it is avaliable, but so far no one has figured out how. Maybe they forgot to add that feature....

You can only use them in campaign/skirmishes by activating the skulls. All they do is look cool anyway...