Hi Umesh,
Are you ready with your letter heads with the ABC P.Ltd with logo etc. If yes, you can issue the offer, mentioning the fact (as 'in the process of registration'). There is no harm. After all some employees are required to carry out the formalities of registration itself, isn't? Such advance preparations, such as preparation of docs like Memorandum & Articles of Association, formation of Board, share capital mobilisation, PAN, address & ID proof, readying the premises, pre-production arrangements etc. have to be arranged before filing application for registration and gets regularised once ROC certificate is recd. & commencement of operations. There is no impropriety or illegality in doing so. All these expenses, fees etc will be treated as "Preliminary Expenses" and amortised in due course. Even for filing of application for grant of factory licence also so many docs have to be filed. Who will do all the formalities without engaging the required personnel.