Even for "just fillers", you may not have enough of a comfort level to do a high volume without a fellowship. There are multiple dermatologists in my group who won't do Radiesse or Sculptra or Voluma or even fillers of any sort because they haven't done or seen enough cases to feel comfortable handling a complication. This can be area dependent as well as more competitive areas tend to have more finicky patients who will look into your background before allowing you to do any cosmetic procedure. Even if it is something as simple as Botox or filler.
Cosmetic dermatology may also include liposuction, fat transfer, any array of lasers, blepharoplasty, sclerotherapy, chemical peels, and any number of other procedures. If you are lucky enough to gain enough experience to them during residency, great. I would not go about selecting a residency based solely on what they can offer cosmetically though.