You mean the Slider widget? The Blizzard UI uses XML for all of their windows/options. I'm fairly positive you can do it.
You don't need to use a library to make config windows. And you don't have to use XML (you could write it all in Lua).
That said, I create my larger, more extensive option windows use AceConfig. If the addon only has a few settings, though, I write it from scratch.