The staff of the Securities and Exchange Commission agrees that "Counsel may opine on the laws of the states in which they are admitted to practice". SEC Staff Legal Bulletin No. 19 (CF) (Oct. 14, 2011). Oddly, however, the staff will not allow lawyers to make the accurate disclosure concerning where they are admitted (or not admitted):
For example, if counsel admitted to practice in Massachusetts writes a legality opinion under New York law for debt securities in which the indenture is governed by New York law, counsel may not indicate in the opinion that he or she is not admitted to practice in New York or is admitted to practice only in Massachusetts.
It is hard to explain why prohibiting accurate disclosure harms investors. Perhaps the staff views this additional disclosure as a "hedge" by the opining counsel. If that is the staff's view, however, that would be a reason to include, not exclude, the disclosure. If the question is one of competency, disclosure of where counsel is, or is not, admitted is not material. The staff should not prohibit accurate immaterial disclosures.