I don't see why they couldn't be periodically corrupted. However, I imagine it'd take an extremely powerful Darkness spirit to actually corrupt it significantly; take the Frozen Claymore, for instance. If a Darkness Spirit inhabited it (let's say a relatively weak one), it would probably just still weaken Akriloth and use the power of darkness in tandem with ice, instead of solely the power of darkness or ice.
As for the Blade Of Awe, I feel like the same thing would occur; you could still implant Elemental Orbs into it to enhance it's power, though the power of earth, fire, wind, energy, etc. would probably only be, again, somewhat augmented by darkness instead of being completely pure. This would somewhat stifle it's power against beings with resistance to darkness, but granted since it's still the Blade Of Awe you're using, it'll probably still be able to seriously wound them anyway. An exception for this, I imagine, were to be if you implanted the Light or Darkness orb into the blade; Darkness would probably not only work great with the darkness spirit dwelling within the blade (good thing for it, bad thing for us), it might even soak up some of the darkness now flowing throughout the blade and become stronger from it. If it managed to completely fuse with you in this state...well, you're doomed. And everybody else. Same thing if it managed to do so with any other orb (aside from Light) happened to be in the orb. You'd get a being 1 part darkness spirit, 1 part legendary artifact, and 1 part human.
If you just popped in the Light orb, though, I think that the darkness spirit lurking within the blade would pretty much be instantly annihilated. Maybe if it's stronger, it might be able to escape the blade in time, but there's no way the spirit is going to stay into the blade. Good question, though; really makes you think. As for the name? I'd probably call it the Blade Of Dread, maybe?
What would happen if we'd managed to rescue Sepulchure immediately after he was betrayed by the Mysterious Stranger, and enlisted his help directly afterwards?