I discovered two active players who don't feature on any 'best' list but who might be important to the history of chess960: GM Miguel Quinteros, aka mquinteros, and GM Eugene Torre, aka Bradidik. Both are known to have been friendly with Fischer.
After writing that paragraph I started to wonder whether Fischer might possibly have played chess960 on the ICC. There were, after all, rumors that he had been spotted there in the early 2000s. Before looking into the details, I checked whether chess960 was available on the ICC at that time. Indeed it was: ICC News Item #1125, 'Fischer-Random Chess is now available on ICC', dated 15 January 1999.
The Internet Chess Club now has Fischer-Random Chess available as wild variant 22. The pieces start out in one of 960 possible initial positions. Pieces are arranged randomly on the first rank, with the only restrictions being the King must be between the two Rooks, and the Bishops must be on opposite colors.
That was well before the ICC sightings were reported; for example, The third coming of Bobby Fischer? [Chessbase.com], 18 September 2001:-
The story is not going away, in fact it is gaining momentum. Many people believe that Bobby Fischer has returned and is performing miracles on the Internet. Nigel Short said he was "99 per cent sure" he has played Fischer.
The reports attracted so much attention that the ICC put up a help page titled Short's Encounter with...Fischer? [Chessclub.com]. Using the links on that page I located a radio interview where he was asked about the rumors (see Bobby Fischer Radio Interviews '20th, Reykjavik, Iceland, Jan 27 2002', about 2:00 into the first audio clip).
Q: There has been news that you might have been playing on the Internet. Is that true? A: Not true. That's a lot of BS. [...] Q: Nigel Short said that he met someone on the Net that might have been you. A: He can say whatever he wants.
It turns out that the radio interview was the same I once featured in Fischer: 'The *Old* Chess Is Dead'. The question about Short was asked between the two excerpts I gave in that 'Chess Is Dead' post.
None of this rules out the possibility that Fischer played 'wild variant 22' on the ICC, but it's definitely a stretch. If the ICC ever releases better tools to query the game database, I'll take a second look, but that's unlikely to happen soon.