And the OP was specifically asking about diplexing after the node, which would never work.
I was more interested in using the same coax for distribution of video using a modulator on a Joey, but looked at it once, and theoretically partial OTA up to the mid 20 channels or so, IIRC, could live on the same line as moca based on the 500mhz range Dish has reserved for moca. Even if you were in a market with no upper range UHF stations, just throwing an antenna on the line would likely add too much noise into the moca range and potentially broadcast your moca signal to the neighbors. You would need to cleanly inject the appropriate frequencies and basically create your own custom diplexor using filters.
Not worth the headache and risk it wouldn't work in the end.
