Export an object from Blender to LDraw
In the end, I exported from blender to STL file and used http://marc.klein.free.fr/lego/stl2dat/stl2dat.html to convert to DAT. The final result worked well, and you can see the custom part used alongside regular ldraw parts in the build instructions here: https://rebrickable.com/mocs/MOC-68128/seejay/glittering-viper-rainbow-bears-starfighter/#details
The ldraw model was built in LDCad and the instructions were built in LPub3d.