This is a very good article by Ian Russell about the ethics of fieldwork and archiving.
"Working with Tradition: Towards a Partnership Model of Fieldwork" in Folklore, vol.117 no.1, April 2006: 15-32
It's worth tracking down by anyone seriously interested in the issues raised in this thread. I understand Ian Russell has been researching singing traditions in the Sheffield area for many decades and has evolved a kind of practice which involves working out positive outcomes of collecting for the local community as well as himself (and other scholars).
As well as preserving interviews and performances at his university, he helps individuals and community groups archive the material too; offering to contribute copies of his recordings to local oral history projects or else try and arrange CD releases.
(I can't remember if he discusses matters of copyright in the article.)
Anyway, Russell's point seems to be that a collector should be thinking just as much about how their project might benefit the informants as themselves. Right from the start.
Such ethical frameworks are often legally required for university research and tend to encourage this kind of dual outcome. It's certainly the case in New Zealand and I imagine most scholarly researchers in the UK and US would have to also justify their practices in a fair amount of detail.