Allomancy is one of the Metallic Arts, since all of you seem to be ignoring Zas when it was already pointed out that Tears couldn't be Burned on merit of them being flowers.
ALL Allomantic powers come from the metals that are Burned. Being the body of Ruin doesn't make Atium any different from the other Allomantic metals since Atium itself takes the form of a metal. Ergo, it Burns in the same manner as iron, steel, tin, etc..
Can I repeat the world "metal" enough times before it causes an epiphany in some of you?
At this moment in time I feel like filling my post with as much connotations towards the fact that Allomancy is fuelled by metal, but hey, continue the discussion like Zas, KChan and me never said anything.