I don't know if emu oil helps with mild arthritis, that is, arthritis in its early stages. But it does not help with advanced arthritis. I have tried emu oil, among many other natural remedies, and it did not work. It moisturized my skin, but it did not reduce my arthritis symptoms at all.
I also have not seen any studies proving that emu oil works for arthritis. I don't know if any new study has been published about it. I think that emu oil manufacturers often promote the use of emu oil for arthritis for obvious reasons. But if it really was effective as they claim, doctors would recommend it and everyone with arthritis would be using it.