It the courts required more than evidence for impairment to establish the relevance of a victim's 0.21 blood-alcohol level, I can't see them requiring admission of a low-level marijuana level for that purpose alone. I still think it should come in if the state challenges GZ's description of TM looking like he was on drugs.
I definitely thought Martin looked like he was on something at the 7-Eleven, but that could be confirmation bias, I suppose.