However, does DAN then have a legal responsibility, to a reasonable degree, to make sure there are no false claims? If so, whose responsibility would a court likely rule greater? DAN's to do their due diligence or the shops to not make false claims?
With no legal knowledge other than what I make up, this would be my thought: Just like other documents and forms (such as applications for insurance, loans, substitute teacher, TSA precheck, passports, or Global Entry; Federal and State taxes, etc....), a person signs the form to attest that all information provided is accurate to one's knowledge. In some of these cases, due diligence may come in the form a background check or a check of one's credit score. Who know's what the IRS does? I would have to think that purposely misrepresenting yourself on paper is a no-no no matter what the other party does.
DAN spells it out fairly well in their application and seems to cover all of the bases:
"___ was required in the ___ Application to acknowledge, make, and confirm, and did acknowledge, make, and confirm, certain statements and representations in the Declaration Section including, among others, that “all statements and particulars contained in the Application and any attachments are true and correct,” that “no information whatsoever has been withheld that might increase the risk of the Underwriters or influence the acceptance of this Application,” that “failure to disclose any material facts, which would be likely to influence the acceptance and assessment of the Application, may result in the Underwriters refusing to provide
indemnity or cancelling the policy in every respect,” and that “I hereby acknowledge and declare that I have never been suspended, annulled or removed from any dive instructor association or agency and that coverage will only be effective as long as my professional membership is current or I am in training.”
Since all of this is in the written application, I don't think the court will care if there was due diligence by DAN to check on whether the op was truthful or not and that the court would side with the meaning of the written (and signed) document. The responsibility was for the dive op and person's involved to be truthful.