Can project dates be outside of the earliest task start date and latest task end date?

Yes. If you select not to automatically roll up task dates at the project plan type level, then the project start and finish dates are editable. They won't need to coincide with the earliest start date and latest finish dates of constituent tasks.

If task dates roll up the task hierarchy, then project dates aren't editable and always coincide with the earliest task start date and latest task finish date.