"I approve all" No, is the simple answer as you may find family and ancestors already on WikiTree and if you just approved all then you could be creating duplicate profiles. Our primary vision is to build a collaborative tree with just one profile per person.
Click here for the GEDCOM and here for the GEDCOMPare Help pages.
Splitting a Gedcom isn't that simple. The splitting needs to be done at the source -- in the software that generates the Gedcom, or possibly in another software package that is used as in intermediate between the original software and Wikitree. See the "Help: Splitting a Gedcom" page on WikiTree.