Head was point of contact. That's illegal. End of period.
So, this is the language at play:
48.1 Illegal Check to the Head A hit resulting in contact with an opponent's head where the head is targeted and the principal point of contact is not permitted. However, in determining whether such a hit should have been permitted, the circumstances of the hit, including whether the opponent put himself in a vulnerable position immediately prior to or simultaneously with the hit or the head contact on an otherwise legal body check was avoidable, can be considered.
Seeing it again, I don't think Eller actually put himself in a vulnerable position "immediately prior to" the hit. In other words, the onus should be on Gryba since he went for the hit and essentially 'missed' but caught Eller in the head with his shoulder (ie, not because of some sudden shift by Eller).
But listening to CBC panel I'm getting the impression that it won't be seen that way by the head office.
I'm rooting for the Sens here, if anyone, so I'd like to think I'm seeing this objectively.