Can I import data from another app/website into UnitCrunch?

Currently, you can't import data from anywhere other than a file exported from UnitCrunch.

Creating such a feature is technically possible but UC's internal data schemas are still under heavy development so any such feature would only work for a few days/weeks before it needed updating again (which would become very tiresome). I'd certainly consider attempting such a thing once UC's schemas are more stable.