No priest or Deacon could be at the burial of my husband at a National Military Cemetery, though he did have a Catholic Funeral Mass. Should the grave be blessed?

​The priest or deacon at the burial should bless the gravesite. If for some reason this did not happen, it can be done at a later time. Hence, it may be good for you to ask a priest or deacon to come and pray the prayer of blessing with holy water. 
 
This is especially the case in non-Catholic cemeteries and military cemeteries. In Catholic cemeteries the bishop has already generally consecrated the ground. But in non-Catholic settings this is not the case. 
 
Be assured, that the grave was not blessed, in no way affects your husband’s status with God. But it is our Catholic custom that burial sites should be blessed. 
 
A related pastoral problem is that many cemeteries, especially national cemeteries, make it increasingly difficult for us to fulfill this custom. For it is often the case that people are not able to go to the actual gravesite, but are moved off to a separate chapel or pagoda somewhere nearby. This makes it difficult for the clergy to know where the gravesite is, and bless it. Perhaps the National Conference of Bishops can most effectively address this problem since it is a national trend.