Agree with Gary, to me they have the same meaning, though 'helping someone out' to me suggests there is a specific problem that requires help. It might be a shortened version of 'help me out of a hole'. Just 'helping each other' doesn't sound like there is a specific problem, but an agreement to help the other for mutual benefit. So for an italki example, 'helping each other out' might be two people who are struggling with language learning and have an exam coming up. They agree to help each other out of a bad situation to pass the exam. 'helping each other' would be two people who agree a language exchange for mutual benefit, but with no specific problem to overcome.

If anything, the addition of "out" suggests a certain result. A number of phrasal verbs work this way, with different adverbs.

To me, they have the same meaning. I think that the 'out' just serves to give the sentence rhythm, if there is no following subject (e.g. in 'we can help each other to study') you would not use 'out' in that form.