The Safari browser is now supported natively on Dynamics AX 2012 R2 as well as being supported on Dynamics AX RTM with a hotfix. Taken from the updated System Requirements document from Microsoft for Dynamics AX 2012:
In Microsoft Dynamics AX 2012 R2, the Safari browser is supported by default for end-user tasks in Enterprise Portal. To use the Safari browser with an earlier version of Microsoft Dynamics AX 2012, you must install Microsoft Dynamics AX hotfix 268124 (http://support.microsoft.com/kb/2686124). Enterprise Portal supports Safari only for enduser tasks in the portal. Enterprise Portal does not support Safari for developer or system administrator tasks.
The version supported according to the requirements document is Safar 5.1.5 – on the KB article page, the version supported is 5.1.2. Have fun surfing Enterprise Portal on your iPad.