It looked real to me. Longer, too, but not long enough to seem like it was due to hair extensions.
His father, who guested as lodge member Albert on some of the episodes, seemed to have most of his hair, so I think both of them were lucky in that respect. Albert's most memorable moment on the show was actually hair-related. In the tag scene in "Who Am I?" (season 7 episode 5), Albert takes offense when Robert makes a hair joke and gets him kicked out of the lodge steam room.
He must have not bothered to cut it as much as he did for previous seasons, and just make it fit with his look. It's definitely noticeable when you watch the last season.