Got finally the aimtrak gun to register in mame; it is quite a mess to set up axis, but once you get it done you can copy the same string in all the cfg files for each of the game that use the gun as input and you are good to go.
Although I am still not able to get it to work in retroarch. How do you configure retroarch so all the cores will recognize the aitrak device and properly use the x and Y axis?