I have searched the web and been unable to find a rap version of Willie Mcbride. No one else seems to have found it . Therefore the answer to the initial enquiry is to look elsewhere.
As to the merits of Willie Mcbride as a song, this is a value judgement with mawkish at one end of the continuum and a meaningful and moving anti-war song at the other; find your own position on the line.
Historians are still debating whether soldiers died in vain 100 years after the event so I doubt we will resolve that one here. This debate is also current in terms of the worth of soldiers fighting a war in Afghanistan.
John