[mhedstrom]

I managed to finally get it to work by adding a rule specifically on my mail server saying "anything with +omnifocus in the header, leave in the inbox". Once I did that, the Omnifocus rule triggers - moves it to the omnifocus folder, and adds it to the OF inbox. Other people using Sendmail might have this same problem though, so I suggest you keep note of the workaround for it. :)