If a relative has served in the US military they are more than likely on the US veterans Gravesites List.
Remember the person does not need to be in a military cemetery. Any cemetery where a veterans marker was provided should make the list.
My own stepfather is buried in a cemetery in a small town and because he has a veteran grave marker, he is in the data base.
here is an example of what this list provides.
U.S. Veterans Gravesites, ca.1775-2006
about Winifred J Smith
Name: Winifred J Smith
Service Info.: CMSGT US AIR FORCE VIETNAM
Birth Date: 27 Sep 1936
Death Date: 29 Jul 2000
Cemetery: South Morgan Cemetery
Cemetery Address: Morgan, UT 84050
You can see the veterans marker behind the large gravestone.