I just now saw this post...
Yes, I think planting your seeds more according to what the plants need, cool weather crops vs warm will help you make better use of your short season.
And yes, the seeds that germinate at cooler temperatures are typically frost hardy. But then so are some of the others. I started my cabbage and broccoli on the heat mats, because they germinate very fast that way (about 48 hr!). But they are cool weather crops. Once the seedlings get a little bigger and have true leaves, I will move them off the heat mat. Then after they grow out a little more, they will get hardened off and transplanted out into the garden at least a month ahead of my average last frost date.
So they will still go through some frosts and maybe snows, but they will be fine. I also have spinach and broccoli in my garden that I planted (direct seeded in the ground) in October. It is over wintering and has been through lots of frosts, snows, temp in single digits. It is just sitting there doing nothing, but still green. I expect as soon as things warm up a bit, it will take off and give me a very early crop as it did last year.
By planting early and late cool weather crops, you should be able to get more from your season.