Okay, so I'm willing to believe that there is some kind of plan behind all this, I mean for one thing, wolves in Shinto are tied to the Kami as one of the animals used as messengers of Amaterasu (the others being crows) so the whole purification thing, I get. Foxes are a little more worldly, aside from their association with Inari Okami, and I think that's where I'm a little confused regarding how he can see the dead, unless if it was inspired by the clairvoyance that Abe no Seimei (who himself was the son of a divine kyuubi no kitsune) was said to have, to the point he saw through his mother's illusions as a child, seeing the spirits of the dead would be considered an extension of that I suppose. Is it something that's uniquely his or is it a mutation of the bloodline's unique power? Who knows.
I think the big thing is that there has been absolutely no foreshadowing of Rude's biological mother's heritage up until now, the fact that she actually wasn't nobility was just glossed over, a throw-away line, while there has been no hint of any supernatural blood within her. It could just be when when she mentioned fox, it was a reference to a particularly cunning founder of the household...well there's only one way to find out I suppose.
The thing to remember though is that Rude's not a Fenrir, he only has those powers because the spirit of Femruida's son had passed them on to him, so he's just got the heritage of his mother's family naturally. A heritage that somehow allows him to see and interact with the dead, that has now been refined thanks to his training under Ferris.
Edit:
One last thing, I can't be the only reader who has been getting mad Fire Emblem vibes from this whole manga so far, right? Especially with Ferris.