Add2Outlook is compatible with Outlook 2013 in this way: if clients use it but not if replication servers are using it.

It doesn't matter what other clients use to connect, or what smartphones, but Add2Outlook will not connect and use Outlook 2013 at present.  Add2Outlook will work if the replication server has Outlook 2003, 2007, and 2010.  We recommend Outlook 2010 as the replication engine in online mode on a dedicated workstation.  

Also, we no longer have to add the mailboxes to the profile, as it is possible to pick the users from the GAL through the Add2Outlook Console and save the relationship.

Again, Add2Outlook can't be installed using Outlook 2013, but if others are using it to get their mail it works well.