Hi,
No, that is a .NET server control it can not be used inside html content. It could be used in custom feature development but not in plain markup. Even for feature development I think the jQuery accordion is nicer myself and easier to use.
We have support for jQuery Accordion and jQuery tabs used directly in the html content but that is different, no server controls are involved, just markup and some javascript that wires it up based on css classes. The style of the accordion can be affected by setting the JQueryUIThemeName on the StyleSheetCombiner control in the layout.master file of your skin to any of the named jquery UI themes, a list of the names is in this thread on stackoverflow.
<portal:StyleSheetCombiner id="StyleSheetCombiner" runat="server" JQueryUIThemeName="swanky-purse" />
Hope it helps,
Joe