This is confirmation. 
I’m now the proud owner of my three-port MBP M3 Pro (can’t speak to the two-port). Good news! The two very same bus-powered drives connect and mount correctly even with the system cold-booted and running on battery power. Dock no longer required. Yay!
Just another reason to go with the MBP, I think. The airs are undoubtedly beautiful machines, but it does appear that Pros are for pros.