Often the "not supported" versions work just fine. Suggest you test as part of the process. What it does mean is that if you get any error messages, you may not be able to get help with them.
I would however encourage you to move the users - especially the key financial users to Office 2013 as well if you can. The functionality around creating great dashboards etc is so much more enhanced. (see Mark Polino's blog for details: msdynamicsgp.blogspot.co.nz)
Cheers
Heather