I haven't tried training with ancients, but I have used fire wave and it's like 70k exp/hour with 1 def prayer gear.
I wouldn't say it be good xp if i'm honest, remember when you blitzing @ monkey you have alot more targets, unless you log in about 3-4 accounts and brought them all to nmz to make it so you have alot monsters trying to attack you.
If I remember correctly, this was nerfed a while back. If you use the runes inside the minigame it's only half EXP than it would be. You have to bring your own runes to get full EXP. As for bringing multiple accounts, that would work however, you'd have to keep them all from dying, or logging out so that would be pretty frustrating. I think it would be easiest to just burst/barrage the skeletons on Ape Atoll.

