Trying to get my military background check in order.?

I am about to join the navy and am getting my background check info in order. My husband has not seen or heard from his father for about 20 years. My recruiter keeps telling me i need his fathers info but its just not possible. She says it is a must because when she tries to leave it blank in the computer it says "error". Is this true. If his dad has disappeared from his life can it really be that pertinent to MY background check? Im sure people who dont know who or where their parents are have joined the military. How do they do it? and what can I do?