While I expect the right answer is to import the svg via the parts editor, I rarely use the parts editor. Thus I butchered the standard rpi hat to replace that image with Steve's and made a part from it. It won't export (possibly because of the sticky flags in the fpz) but it comes up in pcb view ok (I'm not sure what will happen when you save the sketch, it may refuse to reload).
Pi_Zero_PCB_shape.fzpz (2.6 KB)
You should be able to load this via the open command in Fritzing and it should give you Steve's image in pcb just like the pi shield part in core.