1976 Blazer restoration

I am getting ready to restore my 1976 blazer. I have several rusted areas that I am going to cut out and replace the rusted area with new panels. I was going to BRAZE the panels and then use body filler. I was told not to use body filler on a brazed area is this true? It is the first time i have heard about this. I there any area where body filler should not be used? Like over lead, braze or? Thanks and have a good day. Doc in PA.