It wouldn't have any effect on Snowy Hydro. Anything below Jindabyne Dam is lost to them, the snowy doesn't even flow between Island Bend and Jindabyne, and they didn't get that much rain above Island Bend. That warning was for the lower Snowy.
This should be good for flushing out the river. It’s probably long overdue. SH and NSW get more than their fair share (~95%+) of water that would otherwise reach Victoria.