There shouldn't be a problem with embedding an <object> tag in the tooltip. The only issue I am aware of is that silverlight and flash objects tend to reload when their parent's visibility, display, size and a number of other properties are changed, thus it will happen several times as the tooltips shows because it needs to size, reposition and generally configure its popup. The best advise I can give for the moment is that you simply try it out and see how it works for you. I can also suggest you examine this online demo
, as it shows two different ways to add tooltips to a grid - a manager with LOD (AJAX) and a regular tooltip with content in the markup.
All the best,
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed