I think unless the uploader said something NOT to share at other places, it will be OK if you mention that you got it elsewhere and thank the uploader without to mention who it was.
That is a compromise between mention the uploader name (not all like that their nick is mentioned on the web) and not thanking at all.
Personally I a very happy if I see my encodings uploaded somewhere and it's mentioned by the poster that he got it somewere else. Like raphjd, I don't like my nick being mentioned.