I sort of agree and sort of don't on this one. I'm really sorta torn.
Everyone seems to be fine with Datsyuk spending time at college working on his sports management degree.
They make it sound like it's largely a ceremonial position where he helps out with a couple kids clubs and helps the club understand what part of the NHL really work versus the media hype. I'm pretty ok with that, but if it was more of a job taking his time, etc... then I might have issues with it.
As to the NHL blocking it, I don't think they really can. Are they going to control what every player does with their spare time? Are they going to selectively vote yes or no if each player can hold jobs outside their club position? Many players join charity organizations and jr hockey clubs which potentially could be seen as competition to the NHL as well. Cheli used to spend a fair amount of time managing his bar(s). Doesn't Draper or Maltby operate a gym?
I think how this differs from what Maltby, Draper or Datsyuk are doing is that Ovechkin is being paid as a consultant in another hockey league. To me that's where it crosses the line. Especially if he's helping the KHL understand exactly what works well about the NHL.
The league can't really control what players do in their free time, but it's within reason for them to restrict their employees from working for another professional hockey leagues. If you work for Little Caesar's, I think it's reasonable for them to restrict you from being paid as a consultant at an old Domino's franchise where you used to work.
And aside from the NHL's perspective on this, it's ill-timed by Ovechkin. His team just surpassed the Sharks as biggest postseason washouts, and he's choosing now to spending time helping an old team in a rival league? All of his professional hockey energy should be going towards figuring out how to keep the Caps from repeating what happened this last playoffs.