What is the distance allowed between the exterior PVC discharge of the furnace & the dryer vent?
I dont know of any on discharge. Intake is i think 3 ft.
I think Henry is right about a discharge only vent pipe … as long as you are sure that is a discharge vent pipe (some mfr’s only recommend elbows on the intake pipe).
For intake pipes a lot depends on the installation specifics. Take a look at the installation instructions for the equipment if available, or look in the IRC for some guidelines.
JMO
I don’t see this installation as a big deal. They both vent and I don’t see a combustible issue either.