The ones you want are "Skulling Pogies" made for Crew guys aka rowing teams...
Nylon waterproof outer with a fleece lining. They are for athletes so shouldn't be crazy hot or sweaty and they are designed for rowing so should be pretty easy to get on and off and have the sealed ends that you would want (rather then a kayak style pogie).
I too like to have direct contact with the oars and I've seriously considered getting some of these. I've also had good luck with fingerless gloves. The ones I have are Wool with Polertec lining and keep me pretty warm till they get fully soaked.
I've done Nitrile gloves before too...and agree that they are surprisingly warm just by themselves. With a thin neoprene gloves or some thin fleece I'm sure it would work great.