Thats an interesting point also, that there may be two different types of shardblades, in addition to the difference between Honorblades and Shardblades. This would definitely explain Syl's repulsion, and would also show more of Odium touching the world. I want to believe that Dalinar is not using a "Voidblade" as you called it, just because I feel he should be untouched by Odium, even if he is doing it without knowing.
Do you think that the "Dawnblades" were just corrupted by Odium at some point, and thus created the "Voidblades"? I don't have my book on me, but during one of Dalinar's visions.. he sees hundreds of the Knights Radiant giving up their Shardplate and Shardblades (or Dawnblades perhaps). I remember that the people who pick the blades and armor up then start fighting over them, but I don't remember if there is a description to how the people died. We might be able to determine if that event changed the blades (Odium's touch?), or if the blades are separate from each other in some way. I hope this makes sense, I'm thinking through this as I go.
Page 733, US hardcover version:
"Dalinar looked back at the melee of soldiers rushing for Blades. Many had already been claimed. There weren't enough Blades for everyone, and some had already begun raising theirs up, using them to fend off those who got too close. As he watched, a bellowing officer with a Blade was attacked by two men behind him.
The glow from within the weapons had completely vanished.
The killing of that officer made others bold. Other skirmishes started, men scrambling to attack those who had Blades, hoping to get one. Eyes began to burn. Screams, shouts, death."
So the abandoned Radiants' blades did kill the same way that modern Shardblades do. Maybe being turned against human beings for the first time corrupted them somehow? I don't know. It's an intriguing question.