It's true. They (GCC) started with Super Missile Attack that ran on Missile Command hardware. Following that Atari sued them, and they were "convicted" to create two games for Atari: Food Fight and Quantum.
The GCC guys also developped a hack for Pac Man: Crazy Otto. They probably learned from their problems with Atari, and this time showed it to Midway. They liked it, but wanted different graphics, so Crazy Otto became Ms.Pac Man, which was released without the permission of Namco, which led to some conflicts between Midway and Namco of course......
Later GCC did a lot of home conversions for Atari. I saw a lot of company pictures, I think on KLOV forum not so long ago, posted by a former employee....
[Edit] Here it is:
http://forums.arcade-museum.com/showthread.php?t=103639&highlight=gccThose guys even designed the Atari 7800 !