On Deck Circles

[MNBlue]

We have a local ASA league up here on the tundra that is authorizing the on deck batter to use the defense's on deck circle to warm up. Knowing this is not allowed by the ASA book, where does the umpire's liability end?

I understand the rule book is written for championship play, and that locals are allowed to deviate from the book, but will that deviation also remove liability from the umpire?

We are currently contemplating our options, not wishing to put any players at risk, much less any umpires.

Thanks for you help.