Or is it perfectly OK to publish the dissertation results in the journal paper, even though exactly the same results can be found in the actual dissertation on ProQuest?
The journal article and the dissertation may have one and the same data, but they have different formats, so, it depends on purpose and focus I would like to emphasize.
Because the journal paper must be so much shorter than the dissertation, the paper will likely not be able to contain ALL of the data and analysis from the dissertation. So, you may select a subset for the paper. Some people get multiple journal publications from their dissertations by use of different subsets in each.