@cacophony555: Thanks for mentioning that alternate command for mame4all
COMMAND = /home/pi/RetroPie/emulators/mame4all-pi/mame %BASENAME%
Once I added that to my es_systems.cfg, Galaga ran flawlessly. I did lose my joystick controls and when trying to map them, mame did not recogize my wireless PS3 controller. But I will try and work through that next.