It's known as dormant seeding and it is generally regarded as the second best method for seeding cool season grasses. Fall seeding has the best results. Dormant seeding requires adjustment to and/or avoiding spring chemical applications like pre-emergents. So yes, apply seed just befor the next snowfall and hope there isn't an extended warm up until temperatures warm up and stay warm in the Spring

Actually, I had seeded it in early November - and, checking it during our thaw - it looks like there was no early germination. Should I just leave it alone, or throw on some more seed? (I had also covered the seed with yard raking to protect from cold.) If I dormant seed, should I rake this up first or just toss on top?

Any suggestions for seed brand?

Also - I am alarmed - because I see a lot of yellow on the tops of the grass blades extending into the lawn beyond where I had applied the Round Up. Do you think that the spray has damaged the healthy parts of my lawn?

Just let what you have done ride. The seed should germinate this Spring. When seeding (dormant or not) it is always preferable to seed over bare soil for seed to soil contact. As far as seed brand, there are others here more knowledgeable. I get my seed from a local sod farm.
It's possible that you had some overspray with the round up. It could also just be the grass turning yellow from winter dormancy/sleep.

Thanks, 1950!