It depends on the dyno shop. I've almost always had the techs look for the oxygen sensor and cats on my cars. The bottom of the E90/92 had plastic, but not over the exhaust tunnel, otherwise it would melt.
however, I've also had internal work on my cars (cams, throttle body, head work, etc), that you can't see, so they still ran the car on the dyno and smogged it.
YMMV of course.