it seems to be extremely insolent and indeed rude to call people who collect garbages "orang sampah or garbage people". Same thing goes to calling a vet "doktor binatang" or a housemaid "orang gaji". literally, they have same meaning no matter whichever name you call. however, contextually they bring about different aspect of perception - and different way of acceptance.
so, think again if you want to call people with name - that they might not like it. =)