Thanks for the link, I had seen this mentioned but had not read about it. After looking at the article and paper I am unconvinced about their conclusion.

Morning glory juice is the chemical agent the Maya used to chemically vulcanize the raw latex sap into rubber. Making the sap into rubber involves a laborious working of the juice into the sap so that all of it "cooks" chemically. Ash is not required for this reaction.

If it was being used at all it was being used in a symbolic fashion. Which is entirely possible. Particularly in Tonina.

Tonina was a major center of the ball game for hundreds of years. There were over 30 active ballcourts at one time in Tonina. I can completely believe balls made in Tonina had the ashes of dead ballplayers mixed in them.

Think the Ferengi and freeze dried slices of Blech. I bet there was biig money in selling balls made with real ashes of Kuk mo Balam.