Well, Grolan got beaten up a lot as a recruit because he can't physically match many Orcs in wrestling and fist fights, so if someone wanted to be one of his tormentors (provided they joined the company around the same time as him, a year and a bit ago) that's one potential relationship. He may have taken revenge in some sly fashion at a later date without getting caught. If Nargesh for some reason wanted to save Grolan from being beaten up that could have been another possible relationship, as this point his only positive one.

Grolan probably wouldn't get on well with the tough minded warrior till I die Orcs, though any that wax political or spiritual may find him worthwhile conversation. 

Looking at the characters so far I suspect most would dislike or distrust him, especially Darku who seems to dislike humans particularly, which Grolan unfortunately resembles. Though anyone who uses a sword might be more respectful of his abilities, or distrust him more like Half Face. (I actually didn't realise the similarity in their fighting styles, nor the similar bucklers, weird coincidence. They would be rivals I think.)

The only character Grolan would inherently dislike, or in actuality probably fear is Hallar the Waterfall, who could easily challenge him to hand to hand combat and outright kill him.