It's definitely not a skill, and not just by definition (though that, too). Luck is actually a measurable phenomenon, and hockey is one of the most luck-based major sports due to its fast and fluid nature which invites more chaos than many other sports do.
That said, there is a positive association between luck and skill. The more skilled you are, the more chances you you're given to get lucky, both because your coach will put you on the ice more, and because you are able to create "positive" events at a faster rate than those around you. If you get the puck toward the net more, you get more opportunities for one to pinball around just right. This is why Corsi was a big deal for a while there.
Further, as the worst players in a league become better and the distribution curve of skill starts to become more lumped toward a large average group, luck starts to have an outsized effect. If I play 1v1 against a mini-mite I need no luck to beat them every single time. If I play against a high schooler, I need a lot of luck to beat them every single time, even if they're not quite as good as me. (but who am I fooling?)\
Consider that this means that while the best players are the luckiest, they're also the unluckiest. If you shoot more, you're going to hit more pipes, naturally.
So luck is a "skill" if you're referring to the ability to put yourself in the position to receive it. I would argue that that's just skill, though. If that's not skill, we need to redefine skill, and if we do that, we probably need to redefine the next thing, and the next.