If you need a tiled bitmap, you can use RectangleSkin (or any other graphics shape skin) with FillStyle.Bitmap(). Just set the repeat argument to true.
If you just want to stretch the bitmap to fill the available space (possibly while maintaining aspect ratio), then AssetLoader would be a good option too. You must load the bitmap from the Assets class or a URL, though. You can't pass arbitrary BitmapData to AssetLoader. So that might be a limitation, in certain situations.
I've been thinking about creating some kind of BitmapSkin class that is basically just a Bitmap, but it switches between different BitmapData when its parent component changes states (like a button's up, down, hover, etc. states). If that's something you'd be interested in, let me know.