\documentclass{scrreprt}
\usepackage{enumitem}
\newlist{tabenum}{enumerate}{3}
\setlist[tabenum]{label*=\arabic*.,leftmargin=*}
\setlist[tabenum,1]{nosep,leftmargin=*,before=\vspace{-0.5\baselineskip},after=\vspace{-1\baselineskip}}
\begin{document}
\begin{tabular}{|p{.175\textwidth}|l|l|l|}
\hline
Identifier & Content 1 & Content 2 \\
\hline
\hline
\begin{tabenum}[series=tableLevel1]\item\quad\end{tabenum} & bla & \\
\hline
\begin{tabenum}[resume*=tableLevel1] \item\quad \end{tabenum} & blub & \\
\hline
\begin{tabenum}[resume*=tableLevel1]\item[]\begin{tabenum} \item\quad \end{tabenum}\end{tabenum} & blabla & \\
\hline
\begin{tabenum}[resume*=tableLevel1] \item\quad \end{tabenum} & blablub & \\
\hline
\begin{tabenum}[resume*=tableLevel1] \item\quad \end{tabenum} & foo & \\
\hline
\begin{tabenum}[resume*=tableLevel1]\item[]\begin{tabenum}[series=tableLevel2] \item\quad \end{tabenum}\end{tabenum} & blabla & \\
\hline
\begin{tabenum}[resume*=tableLevel1]\item[]\begin{tabenum}[resume*=tableLevel2] \item\quad \end{tabenum}\end{tabenum} & blabla & \\
\hline
\begin{tabenum}[resume*=tableLevel1]\item[]\begin{tabenum}[resume*=tableLevel2]\item[]\begin{tabenum}[series=tableLevel3] \item\quad \end{tabenum}\end{tabenum}\end{tabenum} & blabla & \\
\hline
\begin{tabenum}[resume*=tableLevel1]\item[]\begin{tabenum}[resume*=tableLevel2]\item[]\begin{tabenum}[resume*=tableLevel3] \item\quad \end{tabenum}\end{tabenum}\end{tabenum} & blabla & \\
\hline
\begin{tabenum}[resume*=tableLevel1] \item\quad \end{tabenum} & foobla & \\
\hline
\begin{tabenum}[resume*=tableLevel1]\item[]\begin{tabenum}[series=tableLevel2] \item\quad \end{tabenum}\end{tabenum} & blabla & \\
\hline
\begin{tabenum}[resume*=tableLevel1]\item[]\begin{tabenum}[resume*=tableLevel2] \item\quad \end{tabenum}\end{tabenum} & blabla & \\
\hline
\end{tabular}
\end{document}
Here is slightly more automated version that results in the same output as shown above:
\documentclass{scrreprt}
\usepackage{enumitem}
\newlist{tabenum}{enumerate}{3}
\setlist[tabenum]{label*=\arabic*.,leftmargin=*}
\setlist[tabenum,1]{nosep,leftmargin=*,before=\vspace{-0.5\baselineskip},after=\vspace{-1\baselineskip}}
\newcommand{\tabenumfirst}[1]{\begin{tabenum}[#1=tableLevel1]\item\quad\end{tabenum}}
\newcommand{\tabenumsecond}[1]{\begin{tabenum}[resume*=tableLevel1]\item[]\begin{tabenum}[#1=tableLevel2] \item\quad \end{tabenum}\end{tabenum}}
\newcommand{\tabenumthird}[1]{\begin{tabenum}[resume*=tableLevel1]\item[]\begin{tabenum}[resume*=tableLevel2]\item[]\begin{tabenum}[#1=tableLevel3] \item\quad \end{tabenum}\end{tabenum}\end{tabenum}}
\begin{document}
\begin{tabular}{|p{.175\textwidth}|l|l|l|}
\hline
Identifier & Content 1 & Content 2 \\
\hline
\hline
\tabenumfirst{series} & bla & \\
\hline
\tabenumfirst{resume*} & blub & \\
\hline
\tabenumsecond{series} & blabla & \\
\hline
\tabenumfirst{resume*} & blablub & \\
\hline
\tabenumfirst{resume*} & foo & \\
\hline
\tabenumsecond{series} & blabla & \\
\hline
\tabenumsecond{resume*} & blabla & \\
\hline
\tabenumthird{series} & blabla & \\
\hline
\tabenumthird{resume*} & blabla & \\
\hline
\tabenumfirst{resume*} & foobla & \\
\hline
\tabenumsecond{series} & blabla & \\
\hline
\tabenumsecond{resume*} & blabla & \\
\hline
\end{tabular}
\end{document}