If he had a wig, surely they would have seized it before his mug shot.
I think he just has unruly hair.
My money's still on toupee/hairpiece. If his appearance most resembles that of witness accounts and additional evidence (selfies, etc) with hair on his head, LE would have allowed his mug shot to be taken with the "rug" on his head. jmo
ETA: No wigs in prison, I assume. But for a mug shot... I think it's likely ok.