It is not possible to generalize about which journals might adopt which policy. Many journals with an excess inflow of papers might well consider the prior availability of your paper as reason to pass over it and allocate their scarce space to another less widely available paper. Again it would be wise to inquire as to the practice of those journals in your field. Of course in many cases what you submit to a journal will be considerably different from the material in your dissertation. The second issue is an economic one and more relevant to book publication than to journal publication.
Many academic books have very small potential sales and are at best economically marginal.
On the other hand, some people will argue that availability on the Web, because people will neither read a full book on screen nor print the whole thing out, acts more like marketing for the work and does not eat into sales of the book itself. Indeed there is some evidence that sales of the book may even be enhanced. These issues are still in the very early exploratory phase and nothing certain can yet be said. It would be my advice to take the cautious view and assume that the publisher with whom you would like to publish your book may base his or her policy on the pessimistic rather than the optimistic view. In any case, it is the extremely rare dissertation that is published as a book without major revisions.