Registration is not required. make sure that he has no other business except dealing in exempted goods. If he has, then on meeting certain conditions he will be liable for registration.
agree with naveen.. keep in mind one more thing... turnover means total of taxable and outward supply... suppose exempted turnover is 18 lac and taxable supply is of 2.5 lac... then reg. is mandatory as total turnover is more than 20 lac i. e 20.5 lac.