usepackage{outlines}
usepackage[inline]{enumitem}
  setlist{nosep}
% The following code comes from the outlines package manual
  newcounter{cenum}
  newcounter{cenumsaved}
  setcounter{cenumsaved}{0}
  newcommand{labelcenum}{arabic{cenum}.}
  newenvironment{cenumerate}%
    {begin{list}{labelcenum}{usecounter{cenum}}%
    setcounter{cenum}{value{cenumsaved}}}%
      {setcounter{cenumsaved}{value{cenum}}%
    end{list}}
begin{document}
renewcommand{outlinei}{cenumerate} % Comment this command to see the change in spacing
begin{outline}[enumerate]
  1 First item - notice the extra spacing after this item
    2 First subitem
    2 Second subitem
   Some text
  1 Second item - notice the extra spacing before and after this item
    2 First subitem
    2 Second subitem
  1 Third item - notice the extra spacing before and after this item
    2 First subitem
    2 Second subitem
end{outline}
end{document}