Celtic Rock was greatly influenced by heavy metal and not to put it in the sequel would be a shame. What other kind of modern rock music has such ties with a warrior culture? I can't see any reason why it couldn't be used.
Devil's Dance Floor-Flogging Molly
Every Dog Has It's Day-FM
Death Valley Queen-FM
Shipping Off to Boston- Drop Kick Murphy
The Fighting 69th-DKM
State of Mass- DKM
Johnny, I Hardly Knew Ya- DKM