there are even 30,000 arabs who serve in the IDF
and there were Greeks in the Persian Army which Invaded Greece 300 BC
Serving in the army is not like doing any other job. The arabs that serve in IDF end up fighting FOR Israel AGAINST Arabs. So in effect they are WITH Israel.
Similarly the Kashmiris who join Indian army will fight against Kashmiri separatists and against Pakistan. What can be greater proof of a Kashmiri's loyalty towards India :)