But what was Javanese culture BEFORE the arrival of Hindu/Buddhist infuence?
Same as US and Europe.  Very primitive.  Too bad we cannot ask Java Man 
 
I consider most of the keris in my collection to be personal and ceremonial. Even so, what would be the danger of feeding a keris that is souless and not powerful? It might be a waste of my time, but why would i need to be careful?
All I can say is what I know of my own culture.  No point in feeding a lion unless you need the lion to be strong for you.