I just tested the GB, GBC, and GBA emulators. They all work for me (with HDMI video output). In case of the GBA emulator (“GPSP”), you need to put a BIOS file into /home/pi/RetroPie/emulators/gpsp/raspberry. See also https://github.com/retropie/RetroPie-Setup/wiki/The-gpSP-Emulator.
