documentclass[convert]{standalone}
usepackage{tikz}

IfStandalone{
usetikzlibrary{arrows,decorations.pathmorphing,decorations.markings,decorations.text,}
tikzset{>=latex}
}
{
% This command does not seem to have an effect in the main document
usetikzlibrary{arrows,decorations.pathmorphing,decorations.markings,decorations.text,}
tikzset{>=latex}
}

begin{document}
begin{tikzpicture}[node distance=3cm,]

%Define main nodes
tikzstyle{main node}=[black,draw,circle,minimum size=2.cm,align=center]

% Draw actual nodes
node [main node] (1) {Text 1};
node [main node] (2) [ left of=1, ] {Text 2};

% Connecting Arrows
draw [<-,postaction={decorate,decoration={text along path,raise=-2.5mm,text align=center,text={|tiny| Bending}}}] (2) to [bend right=-45]  (1);

end{tikzpicture}
end{document}

documentclass[]{beamer}

% It does NOT work with the following line (but it should)
% I don't understand, because the IfStandalone{}{} command should take care of that.
usepackage{standalone}


% It does work if the sort option is enabled
% (Of course, since the 'sort' option ensures that the 'subpreamble' is reprinted)
%usepackage[sort=true]{standalone}


begin{document}

%%%%%%%%%%%%%%%%%%%
% Begin Unit %%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%
begin{frame}
frametitle{Frame 1}
framesubtitle{This one works flawlessly}
begin{itemize}
item First slide with no picture
end{itemize}
end{frame}
% ---------------------
% Notes ------------
% ---------------------
note{
begin{itemize}
item This works
end{itemize}
}
% ---------------------
% Skript ------------
% -------------------------------
mode<article>{

}
%%%%%%%%%%%%%%%%%%%
% End Unit %%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%

%%%%%%%%%%%%%%%%%%%
% Begin Unit %%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%
begin{frame}
frametitle{Frame 1}
framesubtitle{This one won't work because of missing tikzlibrary}

includestandalone{StandalonePicture}

end{frame}
% ---------------------
% Notes ------------
% ---------------------
note{
begin{itemize}
item This works
end{itemize}
}
% ---------------------
% Skript ------------
% -------------------------------
mode<article>{

}
%%%%%%%%%%%%%%%%%%%
% End Unit %%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%

end{document}