I'd like to create an area in the CMS where users can just manage DataObjects -- for instance, "Jobs" or "Venues." These are things that don't necessarily have a view on the front end, so I don't need all the Page controls.
Also is there a way of omitting a page type from the Create dropdown menu?
For managing dataobjects usually theres 2 ways - Using tablefields, complextablefields etc on the page or adding a tab to the cms with GenericDataAdmin or LeftAndMain - http://doc.silverstripe.com/doku.php?id=genericdataadmin. Theres not too much helpful documentation on genericdataadmin but some of the modules use it so with the brief doc linked I suggest you dig through some of the code and copy that as a base. See the CommentAdmin.php file in cms/code/ for an example of LeftAndMain and try downloading the polls module for a example of managing a Poll Dataobject with GenericDataAdmin