I would definitely recommend having your Ultherapy treatment first. Ultherapy can melt fat if doing a deeper treatment. But, more importantly, I would allow the Ulthera to tighten your skin as much as possible with little resistance before you have it further filled and tightened with fat grafting. Good Luck
It is best to do Ultherapy before facial fillers in general, including fat grafting. Tightening the skin envelope and underlying structures first will help lift things back into place. Plus you don't want the Ultherapy to melt or damage any of the newly grafted fat, so do it first.