Or is it to early to start forcing my players into these channels. Maybe too much of a "good" thing? Should the players take corruption checks when they are in the presence of Gregor? Do I make the rolls secret?

thanks

I use disease and corruption throughout my campagins, its not warhammer without that grim gritty reality, ive not played e4e but I imagine exposure to the picture, ritual, reading the books for corruption, disease is far easier....

As regarding passive tests, my players roll but they dont know why, and with disease/corruption I dont always make them test at that time, I just mark it and give them a test later so they dont know why or what? Sometime though when using warpstone to channel magic for instance the test is immediate.

Hope that helped. Crimsonsun