Under the Dark power heading in the sorcery section in the radical handbook it states that after manifesting sorcery you get 1d10 corruption points minus your willpower bonus.

My question is are you able to reduce the corruption gained to zero, or is the minimum you can get 1 point even after modifiers?

If it doesn't mention a minimum explicitly, there's no minimum, so zero.

Yep, add in a "Dark Pact" and "Armor of Contempt" to cut corruption down even further and you're gonna go far as a sorcerer, barring getting caught!