I found a topic about this exact thing for the SQL Reporting Services Nevron charts:

http://forum.nevron.com/shwmessage.aspx?forumid=4&messageid=3315

I have data labels that contain dollar values which have a tendency to overlap. How can I rotate the labels to 90 degrees so that they don't block each other out? I see no orientation option in the "text style" field in the data labels tab.

Yes, the labels can be rotated. However, this property is currently not implemented in the chart webpart designer and it can be configured via custom code.

If your data labels are overlapping, you should try the automatic data label layout which is controlled from:
Chart Areas >> General >> Labels
Pivot >> Data Groupings >> Values >> Data Labels Layout