A boost test on a duramax would also reveal exhaust leaks in the engine bay correct?
No, the stock cam has 0 overlap, so there isn't any possibility of having both an intake and exhaust valve open at the same time to pressurize the exhaust. Plus, it would just blow out the tailpipe.
Odds are you will have one or more cylinders with the intake valves open, so you can see how much boost leaks past the rings. On my stock motor, it was basically 0 (couldn't hear or feel any air coming out the PCV or oil fill). With my built motor with loose rings (on purpose), I can hear some air blow past the rings, but can't feel it coming out anywhere.
To check for exhaust leaks, you'd basically do the reverse of this, and pressurize the exhaust from the tailpipe. Not sure what you would use to seal to the end of the exhaust, though.