It's very hard to comment without making some assumptions here, since we don't know the particulars...
But I don't see anything necessarily underhanded about quitting on day 366. He didn't take the job with the intent to quit at the 366th day. I don't know the whole picture, but let's assume he produced good work, slowly became disillusioned as the job turned out to be something other than what he reasonably believed it would be, and finally decided to leave. If some of your pay is in the form of deferred compensation (ie., for staying a year), and the writer continued to work honestly at the job (even if he was not highly motivated anymore) I don't see anything wrong with deliberately quitting on the 366th day (at my last startup was 25% vesting per year - in this case, this scenario is anticipated as part of the employee agreement).
Similarly, I'd see nothing wrong with you firing an employee prior to vesting if it turned out his performance was far lower than you reasonably expected it would be. The underhanded thing would be intending to do this when you hired him (then again, this seems like such a loser move... I know projects start and stop, but it seems like the startups that are going to make it have the opposite problem with talent - how to I keep this guy here now that he's vested?)