Options trading using margin as collateral on Vanguard vs Fidelity vs Schwab

On Vanguard, when you get approved for margin, you can use the margin cash you receive as collateral for shorting puts. You can do this on trading level 2, which means vanguard does not consider shorting options using margin cash as a 'naked' or 'unsecured' position, since to be able to trade naked puts you need to be approved for trading level 4. Is it the same on Fidelity and Schwab, where you can use margin cash to as collateral to secure shorted puts, without it being considered a naked or u