1) have enough money to buy robots instead and get rid of the legal and logistic trouble

2) would want to use the dolphins for activities that grant a better return of the investment like marine engineering or war (mining/demining).

Every major of a coastal city in California, or South-Africa (with a big beach visited by thousands of swimmers a day), would pay solid money for bay-watching and shark deterrent services that really work without the need of eyesore nets. People love to swim with dolphins too so would be another tourism resource in itself.

The time of your dolphins would be just too valuable and expensive to do Archaeology.