Using Blender and BRL-CAD to import/export SU2 mesh files. Hopefully one day SU2 can be integrated to work within.
BRL-CAD: You would need to update the CMakeList.txt in src/conv directory in order for cmake to pick it up, and add it to the building process. However, using the program is as simple as adding -o "output-file-name-desierd.su2" "db.g" "object-withen-g-file"
Blender: Add your file as a python script, it is based on the template scripts, so it should act the same.