A non-scientific poll was conducted on this site asking users "Do you have driver monitoring cameras installed in your vehicles?" Here are the results.

Of the 135 responses received, 24% (n=32) stated yes, your organization does have driver monitoring cameras installed in your vehicles. 76% (n=103) did not. 

VFIS published a list of driver monitoring capabilities from a number of manufacturers. See the supplemental resource item referenced on this page.