There are usually lots of things needed to use Telerik controls, Web.config settings, you may need to replace ScriptManager in layout.master with the Telerik one. I can't really offer support for Telerik products but there is no reason you can't use them in mojoPortal. If you use the forum search and search for Telerik you may find some tips from others who have managed to use Telerik controls.
Things can be tricky with dynamically loaded controls, when you consider that the ModuleControl itself is loaded dynamically and then your custom UserControl is loaded dynamically inside it. In some cases it may be easier instead of loading your inner UserControl dynamcially to just embed it directly and set the .Visible property on it to true when using it and false when not using it. Then internal to your usercontrol make sure it isn't hitting the database except when it is visible.
Hope that helps,
Joe