It depends on whether or not their mother actually deserves the hate. If she was a lazy alcoholic who didn't take care of him properly growing up, then obviously he has his reasons and that wouldn't really be a red flag to me in and of itself. But sometimes situations like that can just turn people rotten but that's another story.
However, if his mother tried to raise him properly and obviously cares about him and he still hates her, then yeah that definitely sets off some red flags. Especially if he's mean and/or disrespectful toward her. If a man can't even love his mother, then odds are he won't really love any other woman either.
Generally speaking, men who have good relationships with their mothers are more likely to make good partners, but there are exceptions. Case in point, I had a friend who dated a guy who was a bit of a mama's boy, and yet he was an absolute dirtbag. I have another friend from college who doesn't get along terribly well with his mother, but he's a really great guy.
no it depends on what there mother was like. my mom was very cold uncareing and munipltive. I was hurt in the worst way you can hurt kid when I was a kid over and over agin from 6 to age 8 by a babysitter my mom told me to forget it happend nouthing would be done about it since it was a 18 year old girl that did it and her mom was my moms best friend to this day I will not let older women tuch me. my mother forsed me to do sports I hated it I had to do outher things I did not like to make her look good and god for bid I messed up my dad was not around much he was in the navy. so to anwser your qustion no if a guy dose not like or hate his mother its not a bad thing.
i don't like my mom at she is gone now she passed in 1997 when I was 19 but I never hated her
Its a good idea to understand the relationships in his life. But worrying about that sounds a bit short sited(or unnecessary). Of course if you want to focus on mother issues, good luck. I would be more interested in all.