I managed to get this to run on my Linux desktop without much hassle. For reference, I am using Proton-7.0-3 for this game. I just installed OCP and the roster hack as expected,
as well as the Gold Edition character select menu. The optional character selection is absolutely necessary for the selection stage to render every character. Without it, only some of the original characters render, but all of the characters can still be selected and used. Unless I'm missing something, this mod's default character select stage does not work properly on Linux, since the original game's character select stage still loads. I imagine that the 50 roster hack should work as well, but its default character selection stage would probably be in a similarly broken state. EDIT: Nevermind, this mod's default character select stage works as well with a small change- in the unzipped mod, enter the ui folder then under the models folder, rename "m_team_stage.IGB" to "m_team_stage.igb" without the quotes.
For this game to launch with the roster hack, make sure that "WINEDLLOVERRIDES="dinput8=n,b" PROTON_NO_ESYNC=1 PROTON_NO_FSYNC=1 %command%" is present in the launch options for this game under Steam, without the outer quotes. WINEDLLOVERRIDES is necessary for Proton to properly use the dinput8.dll file. It's unrelated to the mod, but disabling ESYNC and FSYNC prevents the opening videos, menu, etc. from running at 1fps even on an unmodded install.
I also tried to get OpenHeroSelect to work, but to no success. That's probably going to need to run on Windows.