I am sure the game wasn't pirated. Nintendo was (is?) a member of JAMMA, the Japanese Arcade Manufacturer's something-or-other. Also, sources verify that the Nintendo Super System (as the arcade machine was called) was widely released to hype up interest in the SNES, much like the Playchoice 10 before it.
Plus, screenshots of the game on the site I mentioned in an earlier post show copyright information. Very few pirates are lazy enough to leave that kind of thing...