I've actually wondered how close to classic Christian mythology JB is hewing on the Blackened Denarius. I did some research on the angels, fallen angels, etc, and came up with some interesting bits. It's a little far afield of the actual discussion, but it neatly answered the question for me; the question being "Are all Denarians evil?"
Incidentally, this is all based on a couple of research papers by Catholic scholars I dug up on the intertubes. I can't guarantee its validity, but it was certainly well supported.
Satan turned against God, and was cast down. However, he was not thrown into Hell, but was placed as ruler over all of the Earth. Essentially, he became God's dirty work man who serves to test the faith of mankind. Satan is a manipulator, never taking action directly, even in the last days. Incidentally, the Bible never calls Satan a fallen angel, or calls him/it Lucifer, though there is some reference to angels being cast down with a fallen angel associated with the Morning Star, a Babylonian king.
The first angels to fall were known as the Watchers, angels who were tasked to watch over Eden and then the tribes of mankind after Eden. They lusted after the women of humanity during Noah's time, siring the Nephilim, "who strode the land like giants." God flooded the world to destroy the Nephilim, and cast the Watchers into the Abyss to be imprisoned until the Apocalypse. They are led by Abbadon, known as the Destroyer, who serves Satan. The Nephilim were stripped of their flesh by God, and became demons, now existing as spirits to torture, tempt, and lead astray mankind.
After the Flood the 70 tribes of man were rules over by 70 angels, placed as gods (little G) over mankind by God. These god/angels quickly took to fighting amongst themselves (there are some statements in the Bible that suggest that the classic archangels, Michael, Uriel, Raphael, etc, were amongst these gods, though loyal to God). Many of these god/angels turned against God. Thus, Yeshua (now Jesus) was born, lived, and ascended. With his ascension, the god/angel rulers of Earth were removed from power and called back to Heaven. Any who refused would be considered Fallen and cast into the Abyss.
After that, the Bible isn't very clear on angels, demons, etc. Direct interference with humanity (by God, angels, demons, or Satan) was more the arena of the Old Testament.
What I've added on, in order to explain the Blackened Denarius, is that there were 30 of the angelic rulers of mankind who rebelled against God and wished to avoid being either called back to Heaven or cast into the Abyss (which appears to be basically a prison, and not directly related to the pit of fire that is the resting place of bad people). These 30 angels bound themselves to material objects (30 silver coins) using the blood sacrifice of Judas' betrayal and subsequent suicide, and became the Knights of the Blackened Denarius, allowing them to remain on Earth.
The Denarians originally had a goal, which was to short-circuit the Apocalypse. See, in the end times, there will be signs, until eventually the Abyss is opened by the sounding of the horns, and Abaddon, who is called the Destroyer, will rise and rule over the Earth for 3 1/2 years of destruction. Then Yeshua/Jesus will return, Abaddon and his followers (who I've decided are the 20 fallen Watchers and any other cast down angels, though they don't get mentioned again in the Bible) will be imprisoned in the Abyss again, forever.
In my Dresdenverse, the Denarians believe that if they can release Abaddon and/or the Watchers before the appointed time, they can prevent the Apocalypse (which actually ends pretty badly for the bad guys), or at least prevent the course of events that will end up with them all stuffed in a prison for all eternity.
Conclusion: In my Dresdenverse, all Denarians are bad guys, with a goal of unleashing untold destruction on mankind because they want to rule instead of God. Can some be regretting the decision after a few years, sure, but they all committed to a course of action that I think the majority of humanity would call evil.
Wow, that went on long.