if an ECB member NCB has a surplus of revenue over costs, does it still return the surplus to its national Eurozone government?

Yes, see my top-level comment

Deutsche Welle: Germany's Bundesbank Posts Huge Profits for 2008 (10.03.2009)

The entire sum earned is being transferred to the federal government -- which is something of a novelty. In previous years, portions of the Bundesbank's earnings have had to be used to pay off debt from the former East Germany, but now that the debt is gone, the bank's profits will flow into state coffers.

This is because the ECB's equity is owned by the 27 Central Banks in the ESCB and the equity of a National Central Bank is owned by its treasury. However, some decisions have been transferred by treaty to the ECB Governing Council or to the ESCB, and so are made collegially by the NCB Chairmen.

Of all the ways of organizing banking, the worst is the one we have today — Mervyn King, 25 October 2010