Will Ultherapy to the neck make prominent platysmal bands worse or will it help lift them?

By tightening the skin in the neck and jawline, the platysmal bands usually will be more prominent.  If banding is your major concern, you need to put some Botox into them, or have surgery in the neck.  

Neck bands are not easy to improve without having a plastic surgeon do a neck lift and tighten the plastysmal neck bands.  I do find some improvement with botox and microneedling or botox and ultherapy.  I have also had some good success with ThermiTight but this is a minimally invasive radiofrequency treatment but there is downtime with swelling and bruising and it doesn't give the same tightening as a surgical neck lift.
The information provided in Dr. Shelton's answer is for educational purposes only and is not intended to constitute medical advice.  The information provided should not be relied upon as a substitute for consultations with a qualified health professional who may be familiar with your individual medical needs. 

While Ultherapy treatments will create a smoother line to the neck, they can also make platysmal bands more prominent. I typically combine Ultherapy with small amounts of Botox to combat this issue. The Botox relaxes the platysma muscle to reduce visible banding. When the Ultherapy is applied to firm the skin, the result is a very nice smooth neckline. Make sure you are working with a board-certified dermatologist with experience in both these procedures to ensure your treatment is safe and as successful as possible.