Fidelity has pledged that all securities revenue will return to the fund and not Fidelity itself, so no, that isn't the way they (claim, anyway) will make money.

> "Fidelity is not receiving any revenue from the Fidelity ZERO Index funds for securities lending. Nor is Fidelity currently receiving any portion of the income that is generated from securities lent out." --Fidelity August 1, 2018

However, their securities lending practice is significantly less efficient than Vanguard: their total stock market index fund returned only 40% of securities lending revenue to the fund while Vanguard returned 94%. The difference there is in broker rebates -- how much of the interest on loan collateral posted by the borrower goes back to the borrower. For some reason Vanguard seems to be doing a much better job on this (possibly Fidelity is much more aggressive in loaning out shares so receives less benefit).