Did the Buddha work with teachers from other spiritual traditions?
Jatila brothers who had thousand disciples had some relationship with Lord Buddha. But they had evil intentions inside. But Lord Buddha knew their evil intentions. But they soon realized Lord Buddha was superior. Jatila brothers along with their thousand disciples became arhats after listening to Aditta Pariyaya Sutta. You can read the story here. I am unable to recall some other instances where other teachers had good relationships with Lord Buddha, but there must have been.