[Tifone]

Well actually only the demonic troops of Oni don't need supplies, the others do and they are seriously put in danger of starving by the demons' gluttony. Relying on demons' only doesn't look like a good strategy until you have some way to boost the not exceptional MR - having your army of Onis banished by a handful of cheap priests and some blockers looks like a painful experience.
Dai Oni SCs are of course a great opportunity but not until you have some buffs and gear...