If the licence meets the OSI open source definition AND we can use it alongside all our exising non-kernel code (either because its GPL compatible or because we can make an exception for it), we should use it. Otherwise we shouldnt use it in ROS. That doesnt mean we shouldnt use it as a reference source for the thorny internals bits without actually using code from it.
I pesonally am curious to see just what code MS gives out and which bits it keeps secret.