@jan.c.harlan you're running cutting edge stuff, so expect your fingers to get cut
Node_Import work, but very poorly (very basic product fields) for Drupal 6.x and Ubercart 2.x . I wouldn't expect this module to be done, or even start for Ubercart 3.0 yet. I could be wrong, but I very doubt it.
You're getting into mildly difficult stuff and if you don't plan on learning and doing this work yourself, you could have someone pay to upgrade the module for you. Otherwise until someone else decides to move it forward, you are on your own.
You could use Ubercart 2.x and save yourself some grief. I wouldn't expect D7/UC3 to be stable for another 6 months and that's being very generous.