It's not Fidelity's discount. Fidelity participates in the company discount drip.
In your typical drip at a broker, the broker takes drip cash to the open market and buys as many shares (units) as the drip dollars will buy. No new shares are issued in this typical drip.
In ETP's discount drip plan Fidelity notifies the drip administrator of how many drip dollars are due to Fidelity clients. ETP issues new units to the drip administrator at the discount price (withholding the drip cash) The drip administrator allocates the drip shares amoung the various participants (in the ratio of drip dollars) and Fidelity re-allocates drip units from the administrator among its clients.
New units are issued by ETP at the discount price in lieu of distributing cash. Read the 10-K when it is filed. It will show how many drip units were issued in exchange for drip dollars.