Hello Killian,
Does there exist a keybinding for the Ok button?
Yes, it does. C-] activates the Ok button.
If not would it be possible to add it in a CLIM compatible way?
You could add any keybinding to the accepting-values dialog by using "add-keystroke-to-command-table" function. Just provide "accept-values" as command-table argument.
Good luck, Nisar