Forum Moderators: open
If they are parent child categories, then you are unlikely to get two links. But if they are distinct categories, then how close your milkshakes are to Napoleon Bonaparte is in the eye of the beholder.
My advice would be to submit once to both, and if it did not get listings, then forget about it, do not fight it.
I understand from another thread that DMOZ needs more listing for Napoleon Bonaparte ;) )
I'd suggest that the person first submit to whichever of the 2 they thought was the most important listing. If for example they submit for milkshakes and get that, then the can submit for the Napoleon Bonaparte category. Subsequent listeing likely will be harder than the first.