(wait for the second angle for a better view of Kulikov's move)
The second angle shows it all: Kulikov approaches the boards and takes a look at Hertl. Kulikov knows he's coming, yet he still decides to play the puck and turn his back to Hertl, who proceeds to flatten Kulikov. (besides, why do you say that he did not face Hertl at any point? You don't have to face the guy to turn your back to him and put yourself in a vulnerable position.)
Players should be able to assume that as long as they don't put themselves in danger, like Kuli did here, they won't get checked illegally. That goes for checking as well; as long as you avoid illegal checks, you should be able to hit every player on the ice. In my eyes, Kulikov showed horrific awareness by consciously turning away at the last second, knowing how Hertl was coming from behind. Call that gross all you want, but that one is on Kulikov, not Hertl.