IMO at the current scale of Hive, witnesses doing multisig is likely to be unwieldy. The witness set changes, which means the multisig would need to be updated. And getting ahold of witnesses to sign off on spending the BTC during rapidly changing market conditions (which is probably when you want it) is likely to be challenging. Some of this could be improved with software, but developing and auditing software on a limited budget (and a larger budget is unlikely to make much sense for a $1 million fund) is likely to be more risky than just doing it some other way.

I would just recruit 3-5 trusted community members for the proposal.