There’s an updated (February 2016) CRM Online Licensing Guide.
There are some additions for working with Dynamics AX: users licensed with a Dynamics AX Enterprise USL have the right to read CRM Online application data (page 6), and users licensed with a CRM Online Professional or Enterprise USL may read AX application data (page 8).
There’s also a new Voice of the Customer section (page 13) explaining what this functionality provides, as well as the CRM Online USLs required to use different parts of it.
Finally, there’s clarity added to the Add-ons section stating which USLs are eligible to have Add-ons added on.
Get this guide from the Dynamics section of our Licensing Guides emporium: http://bit.ly/MSlicensingguides.