ALLEGIANCE played with Pantera a couple of times and are also featured briefly on one of their Vulgar videos.
METALLICA did not use any Australian support acts, I think they had an Australian busker in the foyer.
Yes ALLEGIANCE played with FAITH NO MORE in 1990 (Real thing tour), the singer you are talking about was only in the band for a very short time, like a few months until Conrad stepped in, most people don't remember or know that line up as the band didnt really do much until those guys left.
ALLEGIANCE also played on the first national tours for FEAR FACTORY, MACHINE HEAD, KREATOR, SLAYER, ROB HALFORD FIGHT (Rob was managing the band at the time), shows with MORBID ANGEL, CARCASS, SOUNDGARDEN, SEPULTURA, KISS, CHANNEL ZERO, SOUNDGARDEN, MUDHONEY, BEASTIE BOYS.. ofF the top of my head..
http://www.myspace.com/allegianceaustralia