Japanese sticks usually mount into metal. The J-Stick that Ultimarc sells is a Sanwa JLW series that originally mounted underneath metal in Japanese candy cabs. ultimarc sells a longer joystick shaft to allow mounting in 3/4" or 5/8" wood.
So yes, it can be straight mounted as long as you use the original short shaft.
Or, you could go the extra step if you plan on using Japanese controls and get a Sanwa JLF or Seimitsu LS series. They are more expensive, but many players consider them superior for 8 way operation.