Basically Underground Resistance recorded a track called Jupiter Jazz in 1992. There are 2 versions of the song, one released under the alias Galaxy 2 Galaxy (Named Hi-Tech Jazz), which was intended for live performances and of course Jupiter Jazz. Both made by the same members of Underground Resistance.
Manabu Naimiki created a homage, in a form of a cover for the second stage of the Battle Garegga game. This is featured in the soundtrack as Underwater Rampart.
Cowboy Bebop also pays homage to Jupiter Jazz, the very song Manabu Naimiki was inspired by for Underwater Rampart. Baring in mind the second version, is also pretty much similar, but none of the composers/artists here used that version.
As far as i'm aware Jupiter Jazz is not in the OST of Cowboy Bebop, but did serve as the basis for 2 episodes, aptly titled Jupiter Jazz (Each part 1 and part 2).
Now i mention Galaxy 2 Galaxy, because the song is very much in line with Jupiter Jazz. Almost close to a remix. However as i reiterate, neither the composer or show creator used this version.
Jupiter Jazz:
Hi-Tech Jazz:
Also here's a clip of performing Hi-Tech Jazz live. Pretty neat if you ask me.
Hope that clears some confusion for you!