Thanks for pointing out those things Darxbane, I think it really contributes to the "Inquisitors use Allomancy" idea.
For the comment about us not really seeing much of inquisitors, I would agree, but also disagree. True, there aren't that many words written where we see them directly, but we do get a lot of indirect knowledge.
In addition, almost every time we do get a good view of them, they are fighting. This goes back to the "what other powers could they have?" theory. When we see them, they are in battle. They have a very very important goal in their minds (capturing Vin, or in MB2, stopping Vin, or fighting for their lives). IMO, if they had other powers, they would use them in this scenario.
Wouldn't that be the one time that we would seem them use other powers (if they had any)? When they were fighting? That makes the most sense to me. Why would they hold back? They have goals they want to accomplish, they are fighting for their lives, they wouldn't hold back. They would use every advantage at their disposal. Thus, I think this also enforces the idea that they use allomancy, and hemalurgy is the process by which they acquire it.
Finally, the other things we have seen about hemalurgy are mostly related to the process of creating inquisitors.
If you think back, there are several references to how inquisitors are made. IMO, that is Brandon's way of leading us to accept the idea that hemalurgy is the process that does that. It's not what they use for thier powers. It's how they get their powers. He wouldn't spend the time referencing the various glimpses into how they are made unless it was an important part.
Also, I think we have to look back to the quote from the Lord Ruler about making them. I don't have the exact words, but I believe it was something along the lines of "Those (inquisitors) are very difficult to replace." He mentions that they are very hard to make. If hemalurgy was simply putting spikes in someone, then inquisitors wouldn't be difficult to replace. Even if some of the spikes were made of pure atium, it still doesn't seem like that would be something that TLR would find "difficult."
However, finding skaa mistings of a particular type, and a keeper that can be sacrificed all to make one inquisitor... THAT seems like something that the Lord Ruler would consider "difficult."