Group Trips, meaning as organized "back home", maybe through a dive shop? You should speak with your trip leader for a coordinated effort. If he just give you a dumb look and tells you you're on your own, you've got a marginal leader. He should also be organizing a tip bucket for the baggage handlers if you're transiting as a group.
Differences in local economies have a distinct bearing on the quantity dollar level. Some destinations (outside of the Caribbean) rarely serve North Americans, this might predispose them to anticipate a tip versus nine at all, as some nationalities simply do not do it by custom or habit.
Feel free to quietly slip special helpers a bit more if you feel that's appropriate. Most of these guys bust their asses for very little straight pay. Boat crew, too. A lot of times we gush over the DM, but who's always hauling your butt back aboard? Take care of that guy.
If your specially hired shore-dive guide isn't the shop's actual owner, absolutely- tipping should be considered.