I'm a very casual observer of UFC but I've never been impressed with anybody's hand skills when I've watched it which isn't to sound like a snob but I'm thinking comparatively to a boxer and when I've been made to compare I've brought up average boxers and the Boxing technique is a million miles apart as it should be. From the chin as you noted, to the elbows, to the feet, to the distance, the angles, the technique of punches, the variation etc; etc; etc;
Yes, he can get away with a poor technique there because your not going to get exposed by a skilled boxer in the UFC. Not at all. You can be exposed many ways, but via boxing skills is rare because there's not even an average boxer in UFC. They stand at further distances because of the different striking and possibility of a take down. Very little mid range action which is where I believe elite level boxers can give Mayweather difficulties.