Gabe was the 271st employee at Microsoft[0] and "was the producer on the first three releases of Windows"[1], so I suppose that, even if he hasn't contributed to the very same code as Bill Gates did, there must be an earlier employee who has. I don't estimate his Gates code number to be more than 2.
Oh I forgot Gabe worked at MS, in that case, yeah, it must be pretty low. Gabe worked both at Valve and MS, and both companies have submitted code to the Linux Kernel.