Hi, 

First a few fixes: 

in supp-pdf change: 

      \font\temp=\gMPa\nofMParguments\space at \size

so, a \space is added. 

in texexec.pl add: 

  $ENV{"MPXCOMMAND"} = "0" ; 

otherwise texexec will loop, due to running mp again and again. 

(or add --nomp to mpxcommand) 

A tip: 

\def\abc#1#2#3%
  {...} 

no %'s are needed after the } here: 

\abc{a}
  {b}
{c}

in case of {} args, tex ignores spaces (unless doing a \write), which is
not the case here.  

Now, here is the solution: 

\def\GraphBox#1%
  {\hbox{\raise1.25ex\hbox{\tbox{#1}}}}

\def\FragA#1#2#3%
  {\NC #1. \NC \vtop{#2} \NC \GraphBox{#3} \NC\NR}

with (a bit minimalized): 

\starttabulator[|r|p|r|]
\FragA
  {1}
  {Eine "Ubersicht "uber den gesamten Stoff der Vorlesung wurde
   am Anfang gegeben.}
  {\SixBox{6}{1}{2}{3}{4}{5}{3{,}7}}
\noalign{\blanko}
\FragA
  {2}
  {Die Dozentin hat sich ausreichend "uber die Vorkenntnisse der
   Teilnehmerinnen orientiert}
  {\SixBox{0}{0}{0}{0}{0}{0}{0{,}0}}
\stoptabulator

this gives an acceptable result, see attachment, which can be illustrative
for others too, 

Hans