Very interesting read and the effort put into it is in itself impressive.
Of course I almost completely disagree and think that Robert Rath is seeing what he wants to see.
I have a fresh memory of the game, less than two months ago of a full non-lethal run.
My impression of The Outsider is that he is a person or force who is generally bored and takes interest in people who have choices and what they do with them. As people have mentioned, the spells he gives you are far better suited to non-lethal gameplay than the equipment you get, so there's no temptation in that, in my opinion.
The Outsider is very impartial.
He sees Daud kill the Empress, but is dissapointed in Daud's guilt and lack of conviction, not because Daud doesn't match up to some evil expectancy, but because Daud didn't think his actions through and suddenly succumbs to his fear of Corvo and the obvious power that the Outsider has given him. Daud is no longer interesting, but what Corvo does with Daud, is.
The Outsider only amplifies your power to choose freely. If the power is too tempting, then that's your own inability to handle it. By Robert's own admission, he barely could. That trio that came knocking on Granny Rags' door? You didn't have to kill them. You could subdue them. That power the outsider gave you to kill people? It only amplified the power of your weapons and what you chose to do with them.
Temptation is a poor excuse for those without strong conviction. Corvo is a man of exceptional skills and power and it's his convictions that are interesting. It's what Corvo uses his abilities for, not how.
"Rivers change course over many lifetimes, and eventually all bridges tumble down. A thousand years ago there was another city on this spot. The people carved the bones of whales and inscribed them with my Mark. Children still find them washed up in the river-mud. Anton Sokolov has made a great study of my runes, but he's not special like you are. He wasn't chosen and he doesn't wear my Mark, so he can't unlock their secrets. Sokolov believes there are specific words and acts that can compel me to appear before him. He searches old temples in Pandyssia and ruined subbasements in the Flooded District. He performs disgusting rituals beneath the old Abbey. But if he really wants to meet me, he could start by being a bit more interesting."
The Outsider couldn't care less that Sokolov is a nutjob who "performs disgusting rituals" or does grisly things to people. The only consideration is whether or not a person is special, interesting.
The pattern repeats. Sokolov is not a person of conviction, merely selfinterested and curious. He's gained considerable respect and is a genius, so he is certainly capable, but he doesn't choose to do anything to change things, in fact he only helps himself through his own power. He's not interested in what Sokolov would do with the Mark, because it would be the cause of Sokolovs choices.
About the heart... let's be honest. It's just a gimmick for you to find charms, explore the setting, the people and history. Throughout it all, almost everyone you meet is a bad person and in a city of bad people, so of course the most interesting person would be the one who rises above all the others. The heart challenges your convictions, sure, but it never tells you what's right or wrong.
So while I agree that the Outsider is testing people, I do believe he's impartial and not just out to see if someone is tempted. He only wants to see the most interesting outcome, the unforseen and the curious (He expresses gratitude every time you spare someone, indicating that surprising him is what he wants. He even states "these are the moments I wait for" upon sparing Burrows, further proving that he is only interested in the unexpected).
I see the parallels between Job and Corvo, they're both stories of conviction through hardship, but I don't see any agenda along the lines of the devil messing with people in the hopes of creating chaos. Chaos is just a biproduct for which the Outsider cares nothing about.
The only thing dangerous about him is that he shows you who you are and continues to let you use the powers you were granted, whether you chose to use them with care or not. All malice comes from people, not him.