Well, you can turn on surface control points for any surface object - but not if you've got an object made up of multiple trimmed surfaces that are joined together. When you've got an object like that it will not show control points because it would be too easy to pull them apart and make their joined edge not touching anymore. There's some information on this in the FAQ here: http://moi3d.com/faq#Q:_Why_does_show_points_work_for_some_objects_but_not_others.3F
But if you get any surface down so that it's just 1 single surface all by itself (either delete other pieces, or use Edit > Separate) and not joined to anything else, then you can turn on surface control points for any individual surface like that.
