Well, the way I figure it, even when Nords are racist, most aren't really racist against Redguard, it's kind of uncommon. I'd think as long as you weren't a Mer, and you really wanted to get into Sovngarde, and you died a warrior's death or whatever, You could likely get in. But who knows, like almost all of TES' divinity and lore, it's really vague and subjective/left up to interpretation.
I see it as:
Say you
want to go to Sovngarde when you die. If you die an honourable death, which is one of the requirements to get to Sovngarde, you go to Sovngarde.
Say you
want to go to Hercine's Hunting Grounds. If you die hunting or whatever it is to get there, then you go there.
I think anyone can go there, it's just that it's a Nord thing to go there. Most Nords want to go there when they die. But, if a Redguard wants to go there, and he dies honourably, then I believe he'll be allowed in.
I'm not saying that this is "set in stone", but this is how I see it.
I could be completely and entirely wrong, which I probably am. But this could explain why the 'Ebony Warrior' wants to go to Sovngarde.
Either that, or another Theory is that he's Completely Dillusional, Mentally Insane, and is trying to make people kill him in a fight to miraculously get to Sovngarde.
