Rearview Mirror - what are these?
 

On the 2015 rearview mirror, on the back driver side is a sensor to adjust the autodimming. Then on the passenger side are a series of holes like a speaker - what's that? I'm planning on installing a dashcam and want to know what I can/cannot block.

I believe they are air holes. some models of the mirror by Mito have an LCD screen in them (backup camera) so there is a fan there.

it's likely they use one mold for all their mirrors. Lexus doesn't make these mirrors, they are licensed, patented, and made by a company called Mito.