I was looking over your code sample some more and I think you could capture to STDOUT if you used backticks or simply do a redirect on the "commandline" like this:

/path/to/your/cdunix/ndm/bin/ndmcli  -x << EOJ >> $log_file
[download]

I haven't tested this all out yet but it definitly looks promising so that I can finally work towards eliminating our Korn shell programs.