Since no one else has answered, I'll take a stab at it.
Yes, I believe that when retrieving an object from the grid, StorageGRID will prefer to return a whole replicated copy of the object rather than having to reconstruct and return an EC copy. However, it depends, largely on where the object data resides. If the whole replicated object copy is at a remote site, and enough of the object fragments of an EC object copy are at the local site, then StorageGRID may choose to reconstruct and return the EC copy.