This is a pre-coffee answer, but with that caveat, I can't think of any examples where dream of/dream about aren't interchangeable.
There might be some cases where one is more preferable or sounds more natural, but I can't think of any cases where they be absolutely incompatible.
One example of preferability would be the novel by Philip K. Dick.
"Do Androids Dream of Electric Sheep?" sounds better than "Do Androids Dream About Electric Sheep?"
There's no difference in meaning, but of course the second one doesn't sound quite as literary or poetic.