Like the other sections on the page, chess960 is split into 'Current' and 'Best' lists. The 'Best' list, identifies the top-20 chess960 ratings of all time. It currently looks like this.
The columns are for ICC handle, player (title / name / elo / age / country), rating, number games. More info on the players can be found using the ICC 'finger' command. For example, the command for the first entry in the list is Finger: Smallville
Information about Smallville(GM) (Last disconnected ... rating [need] win loss draw total best Wild 2232  200 132 7 339 2321 [...] Chess960 2410  75 3 4 82 2480
The difference here between 'Wild' and 'Chess960' isn't completely clear to me. The ICC help page, Playing "Wild" Chess Variants, says
Fischer Random Chess -- Wild 22 This is also a type of shuffle chess, and was invented by Bobby Fischer. [...] See help Fischer-random.
That 'Fischer-random' page starts,
Fischer Random Chess (wild 22 on ICC) is a chess variant invented by Bobby Fischer. To play a game of Fischer Random Wild on the ICC, type "seek w22" to issue a seek, or "match Fred w22" to offer a game to a specific player.
After looking at many finger pages, I'm sure that the 'Wild' line includes counts for Wild 22 (aka 'Fischer-random', aka chess960), plus other 'Wild' variants. Why the separate data for chess960? Again, I haven't figured it out yet.
There's one more thing before I sign off for today. The 'Highest ICC ratings' page says it is updated daily, but there appears to be no archive of previous pages. As with so much information lost from the web, Archive.org comes to the rescue: Saved 22 times between April 27, 2006 and ....
Now that I know a little more about who plays chess960 on ICC, I'll come back to the top players in a future post. There are some well known names on both the 'Current' and 'Best' lists.