Yes, a bald guy can take hair drug testing.
If the person is just partly lacking hair on the scalp, the nurse will just take some of the hair.
For a wholly bald person, the nurse may ask you to provide body hair including chest, armpit, beard or mustache, arm, and leg hair.
Only those who have no hair on the scalp and body can escape from a hair drug test, will be arranged for another measure like urine or blood test though.