The article posted on www.IMFdb.org
states a 5.56mmNATO version was in the T&E phase but never really worked properly
The Predator listing also says the US Army SF(special forces) field tested a X214 mini gun but that weapon was not practical or useful in real spec ops or combat.
The 1990s version of Rock & Roll, the GI Joe heavy machine gunner packed a big mini gun with a canister type backpack for spare rounds. See www.YoJoe.com
The mini gun concept could work in theory but it would be to hard to keep loaded or maintain in the field.
I'd also think it would be what some infantry units call a "bullet magnet".