Max,
Your mileage will vary depending on the version of Android you are targeting. Cupcake/Donut/etc in the 1.x branch don't support HTML5 at all IIRC. Eclair/Gingerbread/HoneyComb and ICS (2.1+/3.0+/4.0) all do much better in terms of support.
The best guide to check is
CanIUse.com. It lists the capabilities of the mobile browsers along side the desktop browsers.