No you can not pass BM objects out. BM will just crash.
If you need objects within C++ do it vice versa by having the class in C++ and create extern types. Those are never handled by the GC so you don't risk a GC crash which is guaranteed if you try to byte ptr your objects (you would need to clone the object data through memcpy and send that byte ptr to the dll ... extra work that can be avoided by using extern types and C++ construction / deconstruction)
If you need objects within C++ do it vice versa by having the class in C++ and create extern types. Those are never handled by the GC so you don't risk a GC crash which is guaranteed if you try to byte ptr your objects (you would need to clone the object data through memcpy and send that byte ptr to the dll ... extra work that can be avoided by using extern types and C++ construction / deconstruction)