Your FG-20 uses Automatic flash metering and you can read about it here: http://www.cs.mtu.edu/~shene/DigiCam...use-A-995.html
In the case of Auto (A) flash, metering is done by the flash itself using an external sensor and not by the camera.
For more on the FG-20 capabilities, read here: http://www.mir.com.my/rb/photography...fg20/index.htm
Personally, I like a lot the FG-20 as it is in essence an EM with added Manual mode.
BTW, the flash that was released as a companion was the SB-19. It uses a system of Auto Aperture setting that is only used by the EM and FG-20. No other Nikon has it as TTL flash metering became the standard in the late 1980s for all subsequent SLR, apart the F55, which is the only AF Nikon not to have TTL flash for external flashes.