Can I use setup assistant to move files to a Mac with a newer OS? I would like to migrate all my accounts, settings and applications from a OSX 10.7 Lion Mac Pro to a brand new OSX 10.8 Mountain Lion iMac. 

Would Setup Assistant be able to move my files to a newer OS?
Yes, you can. Lion and Mountain Lion are compatible in this regard.

You can read Apple's official support document for details on completing the transfer.