This unit cannot be corrupted.

Does his constant effect prevents it from entering play corrupted via Warpstone Excavation/Pleasure Cults? According to FAQ units that enter play corrupted don't change their states:

Q: If I control Fellblade (CC 100) and my opponent plays a unit into a zone containing a Warpstone Excavation (CS 116), is the unit considered to have been corrupted, allowing me to put a resource token on Fellblade?
A: No. A unit that enters play in a particular state is not considered to have changed states. So in this case there is nothing being corrupted to trigger Fellblade. However, if a unit already in play moves to the zone that contains Warpstone Excavation, then it is considered to have been corrupted and a resource token would be placed on Fellblade.

I think not. This is my explanation:

When you play a card, this is placed in a " non zone" where, unless otherwise specified, all effects that this card has, are not yet active.
The constant effects of WE and PC cards, that are being in the game are already active and affect the card, in the "non zone", because they states: "… units enters this zone corrupted … " so when acting their effect, that of the Knights, in this case, is not yet active.

I think you can argue that it enters play corrupted, but then immediately restores itself.  The cards text is just a constant effect that it cannot be corrupted (i.e. cannot be in a corrupted state).  That effect is always active, and "cannot" overrules most other things in the rules.  If the effect said "cannot become corrupted" then I would say that Warpstone corrupts it before its effect is active, but as it is I think his rules text prevents him from being in a corrupted state while he is in play. 

I'd just send it as a rules question though, and let us know what they say.

Entropy42 said:

I don't think that constant effects work when units aren't in play. So yeah, one can say that it enters play corrupted and then immediately restores itself. You're assuming that if card cannot be corrupted it can't be in a corrupted state by any means, however I think it was meant to prevent state changes after card has entered play (and as I pointed out units that enter play corrupted don't change their state).

Thanks for response, as always it's greatly appreciated.