The opinions do apply to national banks -- and to all other banks and thrifts. The FTC is not the regulatory agency for banks, but they are the lead agency for purposes of interpreting the Fair Credit Reporting Act. Thus, their opinions are binding on the other agencies just as an interpretation of ECOA by the Federal Reserve would be binding on national banks, finance companies and credit unions.
As for whether the courts would defer to the FTC opinion, the answer is definitely yes. As the lead interpretive agency, the FTC's opinions are strong legal authority for the courts. And in this context, it is also worth taking notice of the fact that the FTC's opinions took existing court decisions into account, so there is already case law that is consistent with these opinions.
Now for your examiner. The examiner may not have gotten the word yet. Never count on an early opinion before policy is set. In the context of setting policy, there are discussions going on now among the bank regulatory agencies about how to enforce these interpretations. There may be guidance in the future -- and it is not outside the realm of possibility that there could be some modifications. But don't count on it until you see them. For the time being, what the FTC says is law.