Hello Lionel,
On z/OS, vimdiff can be used as a merge tool for Git. Unfortunately the mergetool command itself seems to have an issue on z/OS, failing with an error message even before running the merge tool.
As for using ISPF tools with Git, I don’t see how this could be implemented. ISPF tools require an interactive ISPF session; however, the 3270 terminal is unavailable when ISPF is called from within USS. Even if you call ‘git mergetool’ from a Rexx script under ISPF, and Git calls ISPF once again (an ISPF-USS-ISPF chain), that second ISPF instance runs in ‘batch mode’. That’s my understanding - I might be missing something.
Regards,
Vladimir