Mounting a shelf into concrete, with two non-identical anchors (brackets)
Only you can decide if you can live with building a shelf with mismatched brackets like that. To me it would look like a major hack even if it was in the back of the garage or in a closet. 

From a structural standpoint there should be no problem with the mismatched brackets as long as they mounted properly so that the resulting shelf surface was level and both brackets have more than enough capability to bear the load that you intend to place on the shelf.