In short, the UM does address Dark Energy and Dark Matter in future chapters of Volume III, the Universe System. Go to the following link to see a one-page pdf outlining the chapters in that upcoming volume: https://universalmodel.com/wp-content/uploads/2016/10/UM-Universe-System-Contents-10.15.16-1.pdf. We are excited to get Volumes II and III out as soon as possible!
Regarding your second question, UM research has found along with discoveries of modern science that Hydrogen and Helium as individual elements are rare but water as a substance is everywhere. Oxygen by itself is also rare because elements are not created separately as modern science claims.