EI is an income.He paid into this insurance for the simple reason that he mighht someday be out of work.He can use his EI as income yes.But if the EI runs out before they land he will need to prove income again as EI only last for so long.
So apply put him down as the co sponsor and use his EI as an income,but just remember like i sai they may come and ask for more option C print outs later.So if you are smart he would get a job before his EI runs out and send in a new letter of employment for him as you need to inform them of changes.