If a person enters into a transaction on a derivative contract related to EU gas and electricity (such as a futures contract only for financial settlement that is traded on exchange located outside the EU), that person is not a REMIT market participant.
However, according to the European energy market regulator, if that person also enters into transactions, including the placing of orders to trade, in one or more wholesale energy markets, e.g. enters on a physical trade (or derivative) for the delivery of gas or electricity (or transportation of gas or electricity) within the EU, that person is a market participant and has to report all the transactions on wholesale energy products including those trades outside the EU that are only for financial settlement.
This interpretation imposes REMIT reporting requirements on the - quite extensive - category of extra-EU financial derivatives trades and counterparties.