Used properly the use of a Pressure washer is safe. BUT if you point the spray at the roof or any where else for an extended period of time expect to do damage. I have seen the pointed spray of a pressure washer drill through wood.
I don't use the PW on the roof but I have used it on the sides and front with no damage to the graphics.
Just a note about protectants...
EPDM rubber roofing membrane is made to last 20 years or longer and has a 10 to 12 year guarantee depending on the brand. The guarantee does not require the use of any protective 'roof treatment' or 'roof protector' product and recommends only cleaning. Unlike natural rubber (latex) or blends (tires & wiper blades), EPDM does not require periodic applications of any product to protect it from ultra-violet light or ozone.
The statement or implication that you should purchase and apply a product to "protect" your rubber roof the elements is misinformation. Buying and using such a product can be a mistake and may even damage the EPDM membrane.
Glenn and Lorraine, FullTimers
On the road again in a 2005 GMC Sierra 2500HD 4x4 Extended Cab Short Bed Duramax/Allison using a PullRite 16K SuperGlide hitch to pull a 2004 Montana 2955RL 32' 5th Wheel