Feminised seeds are not clones. They still have variations based on the arrangements of alleles. When you clone a plant you're regrowing that same ant without anything going on at the genetic level. When you self a plant you are recombining that plants genetic material. Since plants have two sets of alleles, they will combine differently, even when selfed. So you will get variations of phenotype expression based on dominant and recessive traits that may not have expressed them selves in the mother plant. Yes, you are only using 1 set of DNA, but you're combining it differently in each seed. Thats the way DNA works. It's why even though I have 2 sons, different aspects of my Y chromosome got passed on. Although they may not share the Same X with each other.
Anyway, no, S1, feminized seeds will strongly resemble the mother plant but are not clones and can be used to do phenotype hunting.