We talk about Ardor as a platform. A DAO could live inside this platform, including all the childchains. You are right, the specific Ardor parent chain can not be used because it does not support phasing, but you are not confined in a single childchain. A DAO could hold funds and distribute dividends in Ignis, AEUR, BITS, MPG, or any other future childchain.

Phasing, smart-contracts, dex, voting, etc. are all common to childchains. There is a easy and direct communication among them.