Scenario:
Party bursts into building where orcish scarred witch doctor and his bodyguard are. Seeing the spellcaster, the party casts obscuring mist and uses the door to bottleneck their opponents, making it that the witch can no longer see the opponents and therefore, can't hex them or cast spells at them (other than hoping to get lucky with area effects).
However, what the party doesn't realize is that the head on a spike next to the door is a Sentry Skull, which allows the witch to shift his senses and see through the skull.
Now, seeing is all he can do -- but -- he's still got line of effect on the party because the mist is not a barrier to anything other than sight.
So, then, here's the question:
Can the witch use the perceptions of the sentry skull to cast spells at the party? (If so, obviously, range would be counted from the witch and not the sentry skull) If so, would that involve all spells including ranged touch, or just area and designated target spells?
Further, can the witch use the perception of the sentry skull to hex the party?
Hmm. I was going to blurt "NO", but if you still have line of effect, I can't really see why not. I don't think RAW addresses this.
I would allow area spells and things like magic missile but nothing needing an attack roll.