Do I need to embargo my dissertation if I submitted portions to journals?
The general answer is: No, journals don't consider dissertations as previously published materials.

Some exceptions (that I don't know), may exist. If you want to be sure, here's a two things you can do:
1-Verify the instructions to authors.
2-In your letter to the editor that accompanies your submission, state clearly that this manuscript will be part of a dissertation.