Hi Arjan,
I haven't tested this with NCrunch myself, but if my understanding is correct, there shouldn't be anything in NCrunch that would stop this from working.
The integration with SpecFlow works via xunit/NUnit/MSTest. Basically, Specflow generates backing source files that can then be run by NCrunch through its standard integration with other frameworks. Other than triggering a build step to automatically regenerate these files when it builds your project, NCrunch does very little to enable SpecFlow to work.
If you're able to supply some example code and/or steps to reproduce, I could help to investigate this issue further.