In order to achieve the desired behavior you can use the actions.action configuration.
In the callback function, you can implement the needed validation.
In the linked Dojo example
a DropDownList is nested in Kendo Dialog. When the 'OK' button is clicked, the text of the currently selected item is retrieved. In case the text is shorter than 10 characters, an alert will appear and the returned result will be 'false'.
I hope that the provided example will be helpful.