It's unclear to me whether or not Apple uses Intel firmware for the non AMT portions of ME. I will report back to you when I find out. However, the evidence I've seen so far isn't looking too good, and it definitely looks like the vast majority of macs made in the last 5 years are all vulnerable, many appearing to run outdated Intel firmware to boot -- not good for Apple.
The evidence can be seen here,
where some people run a python program to check the version of their ME firmware (which works and returns numbers completely consistent with Intel firmware numbering). I wonder if Apple just isn't aware of the hack yet?