I had the same problem on retropie 3.4, with my bluetooth adapter (ID 0a12:0001 Cambridge Silicon Radio, Ltd Bluetooth Dongle (HCI mode)), which I solved by doing the following:
– modify the file /etc/default/sixad: replace LEGACY=0 by LEGACY=2
– reboot (I even had to unplug the power supply)
– connect my ps3 controller via usb until emulationstation has started
– disconnect usb cable and press PS button, it’s connected!
And repeated the two last steps for the second controller.