It is safe to combine Ultherapy and filler treatments together, and it is often synergistic to do both treatments to create a soft, natural rejuvenation of the face.
Ultherapy is a US FDA-approved, non-invasive treatment that uses focused ultrasound energy to lift and tighten skin through stimulation of collagen production whereas fillers restore facial volume loss though aging.
There is no clinical studies that prove that Ultherapy or HIFU will dissolve fillers. To the contrary, in my experience, fillers like Radiesse and Sculptra can work synergistically with Ultherapy to stimulate collagen production.
If possible, I would perform Ultherapy before filler treatment but some physicians prefer to do fillers before Ultherapy, either way is fine.
Hope the above helps!
Cheers! Dr. Terence Tan