I am setting the limitations programmatically, so I can't really hard-code some values into a client-side function and check against that. I can't really tell what Client Events occur when the input is not within the range, but I would imagine that's the approach I would need to take here.
One Suggestion is that you can programmatically find a range for RadNumericTextBox and assign those values in HiddenField, then compare those values with the RadNumericTextBox value in OnValueChanged event. Please have a look into the sample code snippet which works fine at my end.