It wasn't that hard to suspect that those black spots were no good. A quick visit, trying to pass through would suggest as much. I think Soren Calanar might have been a bit leery of working with the Undead, but it seemed like Dilgaard Gamlel, Shae Nosferatus, among maybe others, bought the idea that the Undead were here to help. In a way, it might not exactly be wrong. In all things there is a price after all.