Setting coin_impulse to 10000 fixed it. Hah! I'm still confused a bit though, does this mean people who own espgaluda and ketsui pcbs can't get credits working with a normal Japanese coin mech? Or are the mame drivers incorrect for those two games?
After some investigation, I now understand how it works - And the value of 10000 is WRONG.
coin_impulse is calculated by the number of frames per second the game runs at (Refresh rate)
The game Ketsui (ket) runs at refresh="59.170000" (Lets just say 60fps to make it easy).
So for a 1 second coin pulse, The value of 60 should be used.
1 second coin_impulse 60
2 seconds coin_impulse 120
4 seconds coin_impulse 240
WARNING - The coin impulse is a "BYTE" meaning it has a range of 0-255.
Any values over this may be either cycling 256 or unpredictable.
(Example the value of 256 gives NO coin_impulse and increments up the same as starting from 0)