They "copied" (reimplemented) the SNK IC through reverse engineering. Their actual implementation is through a small ASIC, which is logically equivalent to the SNK/ADK chip ZMC2/PRO-CT0 character data multiplexer.
The converter's biggest problem seems to be that the multiplexer doesn't successfully follow the timing of the original MVS hence the adjustment screw hack. It's possible that all the MVS signals aren't implemented either, as indicated by the non-connected pics, but this would only prevent VERY obscure protected games from working (possibly none).
Most boots are implemented like common carts, even if they have protection, so the issues are really just electrical. This boot certainly doesn't have any protection (the CPLD is just to replace the NEO-273 chip), so there's no reason it shouldn't work at least partially on the converter except insufficient supply current.