In 6.5 there was a terminology change. The term "data model object" was replaced by "data model dataset." Nothing about the functionality actually changed. Splunk is just clarifying that data models are in fact made up of hierarchies of datasets.
Nothing has changed for Pivot with regard to how it works with data models except for this terminology change. Previous to 6.5, you had to select a data model object and open it in Pivot. Now you select a data model dataset and open it in Pivot.
The concept of datasets was formally introduced in 6.5. You can use the new datasets functionality to work with three new dataset types. Two of these types already existed as knowledge objects: lookups and data model datasets. The third type, table datasets, is new to Splunk.
For more information about dataset types, see http://docs.splunk.com/Documentation/Splunk/6.5.0/Knowledge/Aboutdatasets
One difference for Pivot now is that any dataset type can be opened in Pivot. You can do this from the Datasets listing page. For more information see http://docs.splunk.com/Documentation/Splunk/6.5.0/Knowledge/Workwithdatasets#Open_a_dataset_in_Pivot
