These both values a totally different in their state (and behavior), so they cannot be combined.
Unfortunately with RIA services the problem is a little bit more complex, since all built-in (RIA) validation is asynchronous by default. Usually if you set "InViewMode", then the end user will be able to move to another cell (even if the edited cell has an incorrect value due to some DataAnnotation attributes), but row (item) level validation is performed in an async way (via INotifyDataErrorInfo interface) and RadGridView cannot prevent user from leaving "the invalid" row (because there is no result from database yet). RadGridView will show the error (via INotifyDataErrorInfo), but the focus cannot be returned to this row.
However if you have all requirements you can perform a check inside RowValidatING event and stop the user from leaving the row.
Be aware that this check should be synchronous (does not include a call to the database), otherwise the method will be finished and you will not get the desired result.
the Telerik team