Q. Can a student publish their dissertation in part or in whole in a journal?

PhD graduates can publish any portion of their dissertation. Some people even embargo their thesis for a certain period of time to be able to publish portions or the entirety of the dissertation, without other people knowing about their research results before being published in a journal or a book.

The student retains copyright and is free to do whatever they want.
They should alert the publisher that the entire dissertation is available in DRUM (unless the student has already embargoed the document).  The student also has the option of requesting an embargo if it is a requirement of the publisher.