It depends upon the seeker but I think at least initial tracking should be done through a AEW&C if 400KM since fighter radars would fall short in range. However other ways of guiding the missile cannot be ignored.
MTCR is described specifically for unmanned delivery systems capable of delivering WMD, supposing it will not be able to carry any NBC warheards it shouldn't go against MTCR guidelines
:D
Not only ballistic missiles but any unmanned delivery systems capable of delivering WMD. And the Range limit is 300KM.(condition applied)
Report says Brahmos have a range of 290 KM