Since succubus is an actual character type in Disgaea, has anything actually stated that Etna is one? I only ever remember her being called a demon girl, but not a specific type.
She is never stated to be one, and the first game imply heavily she isn't one, by not triggering a specific character weakness vs succubus.
If you mean Laharl he's not weak against succubus he's weak against Oppai and positive statements like world peace. D2 revealed his wet nurse would smother him with her boobs to stop him from crying. Etna and Flonne got mad in the anime when he stated they didn't cause this effect.
