I think an RM would, yeah. Elasa designates a point in the world and says "deathmatch, motherfuckers." An RM would remove the combatants from Gaia's reality, so Elasa wouldn't be able to effect those in it. If you mean Berserker's Rome thing in particular, then I'm not so sure, because that's stated to be a Marble Phantasm, not a Reality Marble. Even if a MP lets you warp reality, you'd still technically be inside Elasa, whereas a RM would shifts you into another world entirely.