If they're running a passive index fund then I wouldn't expect them to be voting at all.
Investment managers are expected to exercise all corporate actions and voting rights unless the Trustee (ETFs are a Trust structure and so there are Trustees) tells them how to direct a vote. If they do, the investment manager must exercise the corporate action or voting right according to the Trustee's direction.
It's all rolled up in the concept of a Trustee's fiduciary obligation to act for in the best interests of the beneficial holder. That last part is very broad and may include actions outside of simply expecting the investment manager to vote or even directing them how to vote.
It isn't as straight forward as many would like it to be.