Safari test automation using Robot Framework via Jenkins
Do you run selenium as a separate process?
I had the same issue if you are not running selenium in the background.

(edit)
Try java -jar selenium-XX.XX.jar in terminal.

After that run pabot or robot command to run the tests.
You can crate app through the Automator and use the same approach you describe to call it from the CI. That is what I end up using.