Here is an example of a CPAP compliance report.  This is from the user/drivers PAP memory chip, usually an SD type card they can produce or report from or their CPAP machine vendor can get it for them to present to their doctors, or a code generated from the machine they can input online to generate the report.

This CPAP compliance report is for a period of 90 days.  Note that usage is greater than 4h/night on at least 70% of nights (89%), demonstrating excellent compliance with treatment.  The AHI is also 3.9, you want to be sure it is under 20.  If it is higher than 20, they may not be well controlled and should be sent for adjustment of their PAP machine settings.
In this case, with good control, I would then give a 1 year certification and check a similar report at that time which should show 70% of the time over a year of minimum 4h/night.
Of course you still want to be sure there is no excessive daytime sleepiness nor any other criteria that would impede safe operation of a commercial vehicle.