I can see not using a plastic tarp in certain areas . Im not sure about ADCO covers except they tend to need replacement more often than a more expensive cover like a Calmark.
If it's a breathable fabric cover like a Calmark , why wouldn't it work ? I always leave my roofvents open with Maxx vent covers on them.
I always thought the main reason was to help with potential uv damage rather than waterproof protection.
I would think a breathable fabric would be ok to use.
However you can't beat a barn or solid rooftop cover.
http://calmarkcustomrvcovers.com/MOST_FREQUENTLY_ASKED_RV_COVER_QUESTIONS.pdf