Could oral cancer hurt if you put salt on it like a canker sore or would the salt have no effect on it?

Yes: Cancer can be an ulcer. Salt on an ulcer can cause pain.

Not necessary: It isn't always painful, so it may go undetected until the late stages. During treatment with chemotherapy rinses with warm salt water is recommended.

No effect: An oral cancer would not be affected by putting salt on it but a canker sore may improve from it (stings like Hades at first).