Can indicators where data are to be collected on the basis of a representative sample (“from rural areas”, “homelessness” and longer-term result) be monitored for all participants?

Yes. Collection and reporting on the basis of a representative sample is a “shall” provision for common output indicators on homelessness and rural areas as well as for longer-term result indicators (Annex I of the ESF Regulation). However, collecting and reporting on the full population is certainly considered as representative sampling.