karstdvr:
What I am referring to, and have seen on multiple occassions,is a cave diver who tags along with an instructor and his class,and lurks in the shadows. In this scenario the extra team member is out of sight of the instructor who is attending to his students.
That method of joining a dive to gain experience is certainly less than ideal. I would use this method only for experienced divers who are or are about to become instructor candidates so they can observe the team and learn how to better critique other divers.
As Kelly suggested - joining a dive where you will not be part of a team and just observing from the dark is not your safest, or preferred option, particularly if you are new and only have a few (less than 100) cave dives under your belt.
Mentoring divers, especially cave divers is a very important responsibility that I feel cave instructors should have as part of their program.
Jumping in and being a part of a team under instruction will help you hone the skills that you learned in your cave classes, if you make mistakes or are inefficient there is someone there trained to observe and tell you to help you be a better diver.
If you join a team under instruction perform as you should then the team you are with is left to make their own mistakes, if you make a mistake then that team will learn from your mistake and be better off for it.
From that analysis I came to the conclusion long ago that having former students in my classes is a win-win for everyone involved.
I believe that if you approach your (or any other) cave instructor and ask him/her to participate in this manner they will be happy to let you, so long as there is space on the team.
One caveat to the above would be for the cave diver I did not train and have never dived with. I would be reluctant to let that cave diver join an under instruction team doing complex navigation dives. I would want to see this cave diver in the cave before I allowed him/her to undertake this type dive with me and my under instruction team.