Just curious....do the sunhallowed/bloodcursed arrows successfully affect the sun over there? If so, when you use the latter, do vampires start attacking Raven Rock/Skaal Village?

Yes it works. No vampire attacks I've seen so far.

as long as you can see the portal to Aetherius you can use the arrows

Yeah, it works.
And it seems to me that Sunhallowed arrows make the sun shoot more rays than before...

ha you know your lore