I've been limiting water to kill off the weeds there, wild onions, creeping charlie and perennial grasses, but that has made all the worms and much of the soil life leave, too. The good news though is that I haven't had any aphids either, which were a bane on my kale last winter.

There are some areas that are badly compacted now from walking, and some area between bareroot tree starts that I won't be able to use for any plants for months. It's too early in zone 5 to seed cover crops, even with a hoophouse.

What can I do in the meantime to encourage the return of the soil life?

Put down a layer of dried leaves, rotted hay, compostable materials and water it down?

At some point, can I introduce some of the "red wriggler" worms from my colony in the basement? The purpose here would be to help compost the matter that I put down--I know they aren't soil dwellers.

The air temperatures in the hoophouse at 4 feet high range from 12 degrees Fahrenheit on really cold nights to high 80s on sunny, warm winter days.

Or should I do something totally different?

For getting worms back in, might as well get the correct ones. Walmart, gas stations, bait shops (depending on location) should have proper earthworms to kickstart things.

You could always consider a vermicomposting trench system to combine your greenhouse, vermicomposting and soil conditioning in one. Nothing to buy, just a way to do larger scale composting inground.
http://www.youtube.com/watch?v=Jl2XybtZ1dA
From redwormcomposting.com