Waymo have in house radar, I think in the 70GHz gap in the absorption spectrum. They're pretty obvious as sort of paperback book sized planes, mounted near other sensors IIRC.
The old Velodyne units were actually susceptible to damage if you left two units running right next to each other. I did hear a proposal at some point for a different but similar unit to use GPS time to sync the rotations of all the units we had live so they wouldn't be pointed at each other, but in practice it seemed to not be a huge issue.
BTW I once gave you guff about continuing to bring up Conti's flash LIDAR, and in retrospect I wish I hadn't, I really enjoy your contributions here.
I went down to Advanced Scientific Concepts in Santa Monica, CA, in 2003 to see their prototype flash LIDAR. It was on an optical bench aimed out an overhead door into daylight, nowhere near a product. It did work, but required strange InGaAs semiconductor processes and a timer chip stacked back to back against the sensor chip. Way too expensive to fab.
I thought that was going to be the future, and that technology would get cheap. But it's still expensive to fab such devices.
Si interpoisers are a pretty mainstream packaging technology nowadays, so that might help with the stacking bits.