Depends really. If someone changed the parent pom specifically to add new elements for this project. They may have only altered the dependency where it was needed.
All in all we should always stick to released parent poms. We have a fast track for releasing the project pom so there is no big issue with staying away from SNAPSHOT project poms.
Maven does weird things when the project pom is a -SNAPSHOT. This is why we have this page here:
I've noticed that the trunk pom.xml for shared-parent uses the old
version of project pom (14, not 15-SNAPSHOT). Compare versions in
those 2 files:
Is it on purpose?