I think its a bug. When I define a cssclass in my aspx and apply it to the radtile of my Radtilelist, the style is not getting reflected. We are working on Q2 2013 version.
This is a bug in the Q2 2013 release and this has been fixed in the Q2 2013 SP1 release of Telerik RadControls for ASP.NET AJAX. Please upgrade your RadControls to the latest version.