Blender 2.8 released.
When pressing Ctrl+G, you are prompted to create a new collection with the selected objects. It effectively creates a hidden collection that doesn’t appear in the outliner. The created collection is still selectable, in the Blender files section of the outliner and can be selected as a particle system source.
You cannot move objects to that collection though using the "m" shortcut unless you dragged the collection from the "blender file" section to the view layer section beforehand. Then it is accessible again.
Summary: The Ctrl+G command in the object view works weirdly, maybe make the new collection be added to the outliner.