It's absolutely okay for you. There is no ban under any law of the land. I think you wanted an experienced person in your staffing, and he could be engaged on a regular basis with a suitable pay scale or consolidated remuneration as your company deems fit, considering his utility value for your firm. Even continuing his EPF is also okay, provided he had previously had one EPF account but not yet closed; the same account could be continued, but no pensionary benefits will accrue to this extended service. Similarly, ESI. This shouldn't be a problem as he might be fixed above Rs. 15,000 scale. To get over this, you may arrange for him a health insurance policy like mediclaim, which should take care of his health needs. If necessary, you have to amend your HR policy/rules suitably to accommodate such a requirement.
Regards.