I could help w/the cold hardiness, but I'm useless for you because I have no humidity, thus roses that suffer from mildew/rust/blackspot I can grow no problems because I don't have that problem at all. Not even my Austrian Copper, which is infamous for blackspot, has hardly any blackspot this year.
Don't get discouraged by the Knockout thread. Knockouts are great for hard-to-grow areas, bloom continuously, and are very hardy. They should work just fine for your situation. It's just that some of us find 'em to be way over used, boring, and aren't "exciting" as far as roses go. But for an area that is hard to grow roses, they'd be a good choice. Also, some of the Canadian series of roses would be fine for your area.
http://highcountryroses.com/Qs...
What I do for my roses (I believe I'm a zone colder than you due to you're right on the coast) is mulch the heck out of them. And since you're looking at just a few roses rather than tons & tons, get a rose collar (
http://www.acehardwareoutlet.c...) for each rose. What I did in the beginning of my rose growing was to get the 2gal buckets that plants come in from Home Depot. cut off the bottom, wiggle the bucket over the rose so that the entire base was covered, then fill up the bucket w/mulch so that only the tips were showing. Worked like a charm. That's not practical for me now as I have over 300 roses and so I'd have buckets everywhere & it'd look really stupid. But if you put down plenty of mulch, that will help.
