I agree with the idea that the person who sent DC to "walk" or search the area and the person who gave him instructions not to call LE if he found Caylee's remains don't necessarily have to be the same person. Could be, but doesn't absolutely have to be.
I see Casey as the possible source for the information leading to searching there, but I don't have any certainty as to the route the information might have taken. If she thought she'd found someone she could manipulate to help her evade responsibility, that's who she'd tell. There's a list of candidates.
On the A/C privilege issue: as much as people hate the idea, I don't think JB was under an ethical obligation, if, hypothetically speaking, his client admitted the crime and the location of the body, to reveal that to LE. I think privilege would prevent that (assuming the communication of the info from the client was made under the right conditions, not waived by the presence of any extraneous 3rd parties, etc.). Beyond that, it gets a lot murkier. I can imagine a defense attorney maybe wishing to confirm his client's story by taking a look, or checking out how likely it might be that the body will be discovered. Could he send an investigator to MERELY look and report back? Could that ever reliably be done without interfering with the crime scene or taking a chance that evidence might be altered or destroyed or contaminated? This is why people connected to the case and who can do so should give their information to LE and let them handle it.