Hi Ajithaa,
There are different practices followed in various organizations. While some issue Offer Letters, some HR have records of their NDA that is taken from the contractor agency. In many cases, it's required to have a copy of their Offer Letters alongwith the personal records, identification proof and NDA.
But yes, if office boys/girls are on direct payroll, their Offer Letters can be issued.
N whatever be the case, sense of belongingness can be strenghtened the way we treat with the people and care them.
Regards
Arti