​The files created for 2D cutting from Nucleo are normal DXF files - you can open them in SOLIDWORKS or this handly free DXF viewer:

The DXFs out of Nucleo will be in whatever units the system is running in, but be aware DXF files contain no measurement system information. When importing the files into another nesting app, you may need to set the units or scale the files accordingly (25.4 or the inverse). 

Nucleo can also create IGES files (2D). To turn that on, go to the CAD Export Options button inside the Nucleo Options dialog on the toolbar:

Check the highlighted option and re-export the CAD files.

Please let us know how this works out.