I've tried out the new official beta drivers on a small test rig, there was no need to apply the 'atikmdag-patcher' patch. With 17.7.1 drivers I get 59Mh/s with beta drivers I get 61Mh/s.
Yes. You need to use the pixel patcher with RX 4XX and 57X cards with a modded Bios. With RX 580's typically you don't need to bypass the signature check.