Do I need to report electricity pass-through to my supplier?

This depends on your contract and what is customary with your supplier: it is not a matter of legislation but a contractual arrangement. Often nothing changes as long as the connection remains in your name and the supplier sends one invoice for total consumption. In cases such as a charging point also used outside your guests, or a property that is in fact split into multiple rental units, things may be different. Therefore, ask your energy supplier whether passing on electricity costs to guests has any consequences for your supply contract, preferably in writing.