Unless you are willing to spray regularly, I'd avoid the hemlock because of wooly adelgid. If it isn't currently when you are, it will be.

I agree with MG that adelgid is a serious consideration.

Would you consider the native white cedar, Thuja occidentalis? They grow in swamps, and are quite tolerant of wet sites.

And/or, if the oaks are thriving, doesn't that indicate that there isn't much problem with flooding in this particular part of the garden?

And, last, we don't know what height you're looking for - are you looking for privacy from neighbors' upper story windows, or ground level views? THat will play a big part in you choice of plants.

If oaks doing good there native kalmias and rhododendrons should live there as well. If you'll go for the mix of evergreens and deciduous shrubs/trees, add clethras that will suck extra moisture, if any.
I have combo of evergreens (kalmias + rhododendrons + azaleas + leucothoe) and deciduous shrubs( kerria + iteas + clethras + buttlebrush buckeye + hydrangeas paniculata) in area where water could stay for a week or so in a spring and for couple of days after the heavy rain in a summer and all of them doing GREAT. Note: kalmias, rhodies and azaleas planted high, probably 7-8" above soil level.
If you will be willing to settle for non-native, but very fast growing screening tree, you might be interested in Leyland cypress (Cupressocyparis leylandii).
Research it well and plant at your own risk as most likely you'll have to prune it more often than you may expect.

What about ilex glabra? Not sure about how tall they get, but they are evergreen and native. ?

I got a Chamaecyparis thyoides 'Andelyensis' for a similar spot this year. It is supposed to be a dwarf pyramidal (slow-growing), but I was under the impression that there were faster growing varieties (species?). At the time I did a little research and I think I recall Dirr calling C. thyoides an under-utilized tree worthy of more usage, but I am not sure, so don't quote me :-)

You might want to try calling NEWFS and ask them to recommend. They are very helpful and ready to answer questions. I called with a question at one point and they actually connected me through to Molina. lol Quite a nice surprise. The stock they sell is superior too with pretty good prices. A lot of small shrubs there are only $25. Everything has always been fresh and healthy when I have bought it there. I am now a big fan. :-)