Don't think that's true. ETF fund managers, when faced with a corporate action decision, will always vote for whatever maximizes their shareholders value.

Courts have upheld poison pills that treat 13D and 13G filers differently. I'd wager most ETFs that hold 5% of major public companies are 13G filers. Vanguard files a 13G for twitter. To be fair idk what the twitter pill will do - maybe it will be more aggressive.