The answer is: it is not possible... but it is not arara's fault.
Infact, the command line --aux-directory is implemented ONLY for a few tools in MiKTeX distribution (it doesn't even exists in TeX Live).
If, from the command line, you run lualatex --help you will get
The following regular options are understood:
--8bit ignored, input is assumed to be in UTF-8 encoding
--credits display credits and exit
--debug-format enable format debugging
--default-translate-file= ignored, input is assumed to be in UTF-8 encoding
--disable-write18 disable \write18{SHELL COMMAND}
--draftmode switch on draft mode (generates no output PDF)
--enable-write18 enable \write18{SHELL COMMAND}
--etex ignored, the etex extensions are always active
--[no-]file-line-error disable/enable file:line:error style messages
--[no-]file-line-error-style aliases of --[no-]file-line-error
--fmt=FORMAT load the format file FORMAT
--halt-on-error stop processing at the first error
--help display help and exit
--initialize be iniluatex, for dumping formats
--interaction=STRING set interaction mode (STRING=batchmode/nonstopmode/scrollmode/errorstopmode)
--jobname=STRING set the job name to STRING
--kpathsea-debug=NUMBER set path searching debugging flags according to the bits of NUMBER
--lua=s load and execute a lua initialization script
--[no-]mktex=FMT disable/enable mktexFMT generation (FMT=tex/tfm)
--nosocket disable the lua socket library
--output-comment=STRING use STRING for DVI file comment instead of date (no effect for PDF)
--output-directory=DIR use existing DIR as the directory to write files in
--output-format=FORMAT use FORMAT for job output; FORMAT is 'dvi' or 'pdf'
--[no-]parse-first-line disable/enable parsing of the first line of the input file
--progname=STRING set the program name to STRING
--recorder enable filename recorder
--safer disable easily exploitable lua commands
--[no-]shell-escape disable/enable \write18{SHELL COMMAND}
--shell-restricted restrict \write18 to a list of commands given in texmf.cnf
--synctex=NUMBER enable synctex
--translate-file= ignored, input is assumed to be in UTF-8 encoding
--version display version and exit
Alternate behaviour models can be obtained by special switches
--luaonly run a lua file, then exit
--luaconly byte-compile a lua file, then exit
As you can see, --aux-directory is not present.
You can obtain something similar depending on your editor, for example WinEdt and TeXMaker have a similar option. See this thread: Is there a way to configure pdflatex to make all but the .tex and .pdf files hidden files?.
08 Aug 2013 16:28:34.563 TRACE CommandTrigger - Command: lualatex --output-directory=.\output\ "Minimalbeispiel.tex"– LaRiFaRi Aug 08 '13 at 14:27araraintegration. – karlkoeller Aug 08 '13 at 14:49