Yes. If they can log in on their own (they were given an email), they manage their own allergens, dislikes, and diet preferences from their own My Profile like any account — the save logic there applies to whichever account is logged in, member or not. As the primary holder, you can also set/edit each member's allergens, dislikes and diet categories for them from the Members page directly; that editing path is restricted to the primary account only.