Teachers don't tend to just give belts to students, regardless of how good they are at grappling. Teachers try to make sure that the student has BJJ training and is familiar with the quirks of BJJ, not just with freestyle submission fighting based on BJJ.
BJJ teachers are just like any other kind of martial arts teacher, they think that there way is better than all other ways and, though other styles can be useful, there's is the best. They usually don't take kindly to freestyle grapplers, but it probably depends on the teacher.
Sig by Toxic
Barnett - Toquinho -Werdum - "Nurmie"
Z. Gurgel - Morango - Rocha - Tiequan