In most flyers and information I have seen on metal and fiberglass type roofing materials, they recommend that you use tar paper along with 1" wood strips to give a gap so that moisture can escape and provide an additional area of insulation (dead air space). You may want to check on the manufacturers website to see what they recommend and then ask them to validate why they recommend whatever it is.
No you need to put down felt paper {tar paper}first then put down the metal. If not you will get water condensation between the sub-roof and the metal. My hubby is a roofer and that's what he said.