Yes, PokerTracker3 supports the Party Mac client - you'd want to check your Party/PokerTracker3 configuration using this guide: http://www.pokertracker.com/products/PT3/docs/?doc=ppconf
Essentially the configuration will be:
1. Install the Party software choosing "English" if offered a language option;
2. Enable the Party option to "save my hands" and note where it says it will put the new hands;
3. Play a few hands (without PokerTracker3) so that it will create the hand history folder;
4. In PokerTracker3's "Import -> Auto Import -> Party Configuration" tab make sure it has the same directory that you noted in step #2.
Then take a seat, click PokerTracker3 "Import -> Auto Import -> Begin Import" and PokerTracker3 should import the hands and the HUD appear briefly afterward. If not click the "Import -> Auto Import -> Start HUD" button and put a check mark in the "Start Automatically" box underneath so it will start by itself the next time.
If you've been doing that or do but it still won't work, see "Pokertracker3 Log Files" at the bottom of this post to enable logging: Basic Mac Install Guide
You want to enable logging then play long enough to capture the problem and return the logs so we can see what's the matter.
To return them open a support ticket here and attach the logs to the ticket: https://www.pokertracker.com/support/newticket.php?cat_id=41