The skin in the forehead and around the crow's feet area is thin, with little room for fillers to plump lines. Collagen was used to fill forehead lines and crows feet long before we had Botox. Unfortunately because the skin is so thin and there is little "give" underneath patients...
If the filler used is injected in the right level of the skin or under the skin there should be no scarring and There is no relationship between hypertrophic scars and fillers
Personally I believe that some products are better for certain applications. Perlane can be used for the lip but it is not ideal for this location. Perlane is a great volumizer but it is difficult to manipulate once placed.
It does not hide well in locations like the lip edge or under eye...