Interaction between Graveyard Busybody and Over My Dead Bodies
Quoting from the FAQ:

What does it mean that &quot;all graveyards are also your graveyards&quot;?
It means each graveyard is no longer under the control of other players. They're your graveyards now, you control them.

Since you are the only controller of all graveyards, the owner does not get to use the creature to block.