There is no way to use it with MAME games unless they originally had some kind of output for a speedometer.
I dont believe this is entirely accurate.
Racing games all have Speedometers. They are already on-screen... so I have no idea why you would want a digital readout.. (Id prefer an analog gauge myself, as well as an analog Tach... ) But.. if one is good at programming, they can do something similar to what Mamehooker does.
Basically, you have to use a tool to analyze variables that the games using. Once you find the speedometer value, you can write a program to monitor that value... and to output a signal to trigger the device.
Thats how the 'cheat' engine works in mame. Someone searches for values, finds them.. then makes a 'cheat' to exploit those variables.
Im no coder. I just know the rough concept of how it works.