Maybe the blood sacrifices releases the power in the Skaa blood, and imbeds it in the spikes, and the Inquisitors sleeping is them drawing more of this power out of the spikes, like the lord ruler, sort of. And thier allomancy is just normal allomancy, but strengthened by hemalurgy. Maybe hemalurgy just superpowers talents that are already there. I think if we're going to assume that Vin is a hemalurgist, we must also assume that inquisitors burn metals, because Vin burns bronze despite the hemalurgic earing that strengthens her bronze. Vin kind of got the bonus here, she's a mistborn, but skaa, so she can still draw on the mist, and she also has the hemalurgic earring to boost her allomantic powers, so she can kind of be both.
Oh, and that could actually make Alendi a potential hemalurgist because he wouldn't need allomancy, hemalurgy just strengthened his natural attributes as a warrior, and proabably increase his healing abilities as well. The one problem with the Vin+Bronze Hemalurgic Earring=Vin piercing copper clouds theory, is that Bronze isn't Vin's only super powered metal, she also has very powerful pewter, if you remember the thug-head explosion incident. Now was the earring bornze or pewter, I can't remember.