As Manager of a Dive Resort in Lembeh I can tell you that there are NO "hard and fast " rules in regard to tipping, however ANY tip that you give will be most appreciated--and is of course given at your discretion based on the quality of the service you received.
However, since the diving is normally the "main event" here, I would be glad to explain how WE handle the tips/gratuities, just send me a PM and I'll give you the details.
I will also add that a LOT depends on where you are from (USA, UK, Asia, Scandinavia etc..) and your personal and cultural experiences...Seeing it from my perspective, it's almost merits doing an anthropological study on the various attitudes towards tipping, and how different people from different parts of the World approach this sometimes "delicate" subject....
Safe trip and happy diving!
HMB