Since the FAA has never defined what exactly it means by "requirements", we don't have any definitive information on this. Arguably, the requirements for a rating are whatever is needed to prepare a student for checkride.
Interestingly, in the latest proposed revisions of the Part 61 regulations, the FAA wants to add the requirement that an instructor be a -II in order to provide the instrument instruction required for a Commercial Certificate. This has already been the interpretation by the FAA, but they seem to have a need to put it in the regs. This also casts doubt on the FAA interpretation that any "instrument instruction" requires a -II; otherwise, why the need for a regulation change. Anyway, I made a comment on the NPRM website that they officially define instrument instruction as something that requires a -II, since that would be in accord with the attitude of the FAA.