How exactly does this answer the question?

The set of non-ethical categorical imperatives is non-empty.

I agree. Epistemic imperatives are categorical, but non-empty.

The set of non-ethical hypothetical imperatives is non-empty. Hypothetical imperatives include instrumental rules, you have to use X to achieve Y, game-laying rules, etc.

Right, those are examples where non-ethical hypothetical imperatives often show up.

So how does this add up to a reason to think there is a case against categorical imperatives that doesn't equally well count against hypothetical imperatives?