If you are referring to exogenous siRNA, I think the response is no. If you meant endogenous siRNA then it depends in which model organism you are working with. The presence or absence of an S.pombe Rdp1 homologue (RNA dependent polymerase), which is absent in mammals and drosophila, could be indicative. Remember primary siRNAs could act primers for Rdp1 to amplify original double stranded RNA and generate secondary siRNAs. This is an over-simplified picture.
siRNA ain't itself functional in a genome, it splices into a miRNA, which amplifies while translational procedure. If you asking for copy number, then the answer is NO.