Hi,
You can take a look at my site (http://i7media.net) for examples of how to skin the rating container. I use them on blog posts.
There isn't an option to hide the label but you can use jQuery to hide it. Add this code to the layout.master of your skin after the asp:scriptmanager control:
<script defer="defer" type="text/javascript">
$(document).ready(function(){
$("[id$='_Rating_tdPrompt']").attr('style', 'display:none;');
}
</script>
I know this isn't ideal but it will get you by until a css class is added to the rating label.
HTH,
Joe