Hmmm...
Check that the screw hole is clear first, in that case. The old bolt might have seized in there and then snapped off when they tried to remove it, in which case it would need drilling out first and probably re-tapping.
My bolt (2004 model) came out intact when I replaced the hanger last year but it's right in the wrong place to catch spray off the rear wheels and gets rusted in. I had to ease mine out with a lot of penetrating oil and WD40... hence my suggestion to go "stainless" with any new bolt.
If the screw hole is clear then fit a bolt. A self tapper sounds like there's some bodgery afoot.
Ralf S.