Do MIA persons receive Purple Heart awards?

I would have to presume they would meet the eligibility criteria. "Being wounded or killed in any action against an enemy of the United States or as a result of an act of any such enemy or opposing armed forces"

With only the info you provided, I would think missing in action and presumed Killed in action would earn the Purple heart!

You can be MIA for a number of reasons beyond just being captured or killed by the enemy. There were plenty of helicopter/plane crashes from WW2 through Vietnam that happened due to mechanical error or pilot error. Under those circumstances, I don't see how they could be awarded a Purple Heart, as they weren't killed by any kind of enemy fire/accidental friendly fire. And if the person is just MIA, how could you ever truly know until you find their remains?