Oh I wouldn't be that sure. The whole reason Garrosh disliked Val'kyr and Blight was because he didn't trust Sylvanas and the Forsaken to begin with, even though he pretended it was about honor and shit. Same about his little affair with Blackscar.
Garrosh had an actual honor code but was entirely bent over Garrosh's own wishes and desires. Much like Arthas, passion and emotions are what guided him mostly, the kind of characters that stop at nothing to get what they want, whatever it is. Look at Arthas indeed. Beloved prince, heir of Lordaeron, paladin of the Holy Light supposed to uphold honor and compassion above all else, yet he ended up as he did because, despite that, he always put his own desires on the top of his list. And when he had to gradually discard all he was meant to represent in order to fulfill such desires, he simply did. Garrosh is made of the same stuff. He says so himself in War Crimes.