The evidence you sent regarding the support given to Benjamin Ruff's widow, reflects that the local county court acknowledged that he served in the Revolutionary War. This would be sufficient proof of service at the local level. I haven't been able to get to the military records in Virginia to see if I can find him in miscellaneous records, under his name or under an assumed name, thus as it stands, I can't say for certain, what rank he would have had.
I am submitting his name for inclusion in our book, but at the moment cannot tell you when it will be approved for publishing, as research continues. However once I know for certain I will contact you. I have created a file on Benjamin Ruff and will add to it if I find additional information.
Thanks for the update.