Yes with preconditions. First, its gotta be declared a 'Holy War' by united religious authority such as a Caliph. Since we have no institution of Caliphate since the fall of Ottoman Caliphate, one cannot declare Holy War against the infidels and thus claim "rewards" per Hadith by doing violent Jihad
We have no longer any Muslim army. What times are you living in? 7th Century?
What we have now are national armies of 57 or so Muslim majority countries
. They consist of Muslims and non-Muslims alike as non-Muslims also are nationals of many Muslim countries.
Again, BS. There is no such thing as "MUSLIM" army.