Can't myself see why his signature is needed anyway to prove service.Tonywiltshire or Barmaid may give chapter and verse, but my experience has been that In a extreme cases of personal service a process server does it for you and makes a statement that the man identified himself/signed he'd received/ was recognised by the process server from a photograph provided/ by other evidence was demonstrably the man. But in most civil proceedings a court may order substituted service which may be by registered letter to his last known address or by advertisements in newspapers or any other means it thinks fit.
If it were otherwise, every pettily dishonest individual would avoid all legal proceedings forever, and indeed, everyone would be doing it once they realised it worked! Anyway, if this man has solicitors acting, and the solicitors certifies that they will accept service, you may serve on the solicitor.
And yes, 5 years separation is enough, whether consent to divorce is given or not, to constitute grounds for divorce.
With no children involved, the other party's involvement is less, because there's no agreement needed between the parties or no order of the court required for their care and custody etc