The JROK board is much easier and cleaner than trying any of the MultiWilliams hacks. And to answer your original question, no they don't work off of the Defender boardset. The Defender ROM image is hacked to move some of the internal addresses that changed between Defender and Stargate (like the watchdog) in order to allow Defender to run on the updated hardware. Also the Defender ROM board does not have the DMA (Special) chips that are necessary to run the games after Stargate (Robotron, Joust, Splat!, Bubbles).
Final overriding consideration: JROK $175 (IIRC), Clay $250+ (not counting the $120 to get a Joust or Robotron board set to plug it into).
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