Do the drivers have to work extremely long shifts or do they have to work multiple jobs so that fatigue becomes an issue? In that case the camera system is probably not the right solution ...
Driver fatigue is an issue for freight companies of all sizes, everywhere, and use of amphetamines to stay awake has been a frequent practice among many drivers for a long time. This is a freight industry issue, not an Amazon issue.
This review I linked here says:
Individual characteristics were mainly associated with alcohol consumption while poor working conditions were mostly associated with amphetamine intake
So, I don't think that narrative necessarily lines up with available evidence.