But the thing is Nop already did
@(Html.Telerik().ScriptRegistrar().jQuery(false).jQueryValidation(false))
in _AdminLayout.cshtml as suggested by the Telerik team. Perhaps that is some other conflict not resolved by the above line (not familiar with Telerik, just a while guess). Anyway, Telerik Window should work find I guess... so you may not need jQuery UI in this case (unless you have a special reason for using jQuery UI)...
:P