Both.
If the appraiser 'MUST' (as you'll be forced to agree), then the directive is for the appraiser. I'm cool with your assertion that the underwriter has to verify that the appraiser did, but the fact remains that it's the appraiser who MUST, not the underwriter. In which case, the guidance is written for the appraiser.
To carry your logic to its conclusion: the Selling Guide isn't written for the appraiser, thus the appraiser does not need to follow it, because it's written for the underwriter. That is ludicrous.