I was just on a trip and the dive shop owner took all the tips and said, "we will distribute, don't you worry". I don't know if my money ever made it to the workabees.
I never participate in "group tips" because you never know what happens to the money. I know of a dive shop owner who collected a group tip at the end of the week and then told another employee at the shop the guests gave enough so he didn't need to. On all the trips I put together, I never collect a group tip. I will try and find out what is the norm and if anyone asks I just tell them what I found the usual or customary tip to be.