Hi Ben
The uncinate should actually be fairly easy to track (though I am not too familiar with TrackVis, I do my tracking in Slicer). The problem is one of specificity, i.e. to place an ROI such that you only get the uncinate and nothing else is very difficult. I suggest you get a set of tracts first that includes the uncinate and then clean the tracks up afterwards (Slicer has a handy, interactive fiber selection/cleaning tool). For that, I usually place ROI either a) very generously in the anterior temporal lobe, or b) place an ROI is the up-down-ward region medial-anterior temporal lobe; if you look at the color coded FA image, you can see that as a small blue region in the medial & anterior temporal lobe. Option b is the most effective.
Hope this helps
Martin