You should be able to sow Milkweed seeds for a natural stratification outside, and they should also be able to germinate alongside the cover crop. If competition is too heavy between the older cover crop plants and the new Milkweed seedlings, then their establishment and growth might be slowed, but Common Milkweed in particular is so adaptable that we'd expect it would do just fine. Granted, seedlings are always more delicate than mature plants, but as long as they don't get mown-down along with the cover crop (if they stay short enough by the time you need to cut down the clover and oats to not be cut down themselves), then the mingling is probably fine. Otherwise, if you're unsure, start the Milkweed in containers that you can then transplant seedlings out of into the ground once the cover crop has been terminated next year.

Miri