Jabber for ipad is more frequently used with cisco communication manager deployment and hence it uses xmpp for presence which is currently not supported on vcs, vcs uses SIP SIMPLE protocol for presence. so if you are not getting any presence for jabber ipad devices i am not surprised at all.
however jabber for mac should show you presence status and if you are not getting the presence then there would be someother issue. As Paul mentioned start the diagnostic logs on the vcs and check what happens when user subscribe for presence information or open a TAC case.
These are the paths to get to each CCX logs through CLI. They may be helpful if you are having issues accessing RTMT or downloading logs through it.
If you want to download them you have to prefix "file get " and you can add one of the options (re...