If I hire someone to perform a service, whether for a flat fee or for an hourly fee, I pay them for that service. I can see no good reason why I should then tip them for doing what I paid them to do. If they do something way beyond that, then, I'll tip them. For example, the guy who repaired my oven, not only repaired it, but he cleaned parts that were not normally accessible. That warrants a tip. Or the deckhand who carries the gear I would customarily carry, warrants a tip. However, I don't tip the pilot who flies the plane.
If I hire someone to perform a service and they sub that out to someone else, I'll pay the one I hired and I expect they will honor whatever deal they had with the person they hired. If I wouldn't tip the person I hired, why should I tip the one he subed the work to?
As to duckster3d, why would you pay a lawyer $1500 to go to court for you? I'll bet you could get any bellboy in the world to do it for $100. There are plenty of lawyers who would have done it for a couple of hundred dollars. Or you could do it yourself for free. I'd guess you paid the lawyer because you realized you needed some special expertise that others don't have and that without that expertise, you could find yourself in a very bad way. Its like when I have my regulator serviced, I could probably do it myself for free, but I know how important it is that it is done right, so I pay whatever it costs without complaint. We get paid what we do because we fix things when they go terribly wrong. And, its not like we got you into whatever trouble it was in the first place. (I never tell people to shoot other people, so when they do, they should not complain to me about the cost of keeping out of jail. And, I never people get married, so when they do and then want out, they should not complain to me about the cost of getting out.)
If it is a matter of tipping people because they have low paying jobs, that is something they should address with their employers. Let the employer charge me more up front -- assuming the cost does not deter me from going there in the first place. Subject to the foregoing, when I am on a boat dive, if I get anything more than a boat ride and air (if it is included), I tip and tip well. ... Especially where wages are particularly low. I guess my subconscious tells me that it is a way of ensuring that the crew will be available next time I want to dive.