I capture the output of some command-line programs by redirecting their output to a temp file and then reading the temp file. That seems to be portable between Windows and Mac (though I haven't tested it yet with Mac). Exiftool uses standard error as well as standard out, so to capture both in the same file, you'll need to do something like:
exiftool ... > output.log 2>&1
The "2>&1" supposedly has to go last on the command line on Windows.
I looked into capturing the output of Exiftool using the -X option, which writes XML output, and then using the SDK's LrXml to read it. But I ended up not needing to go that route and don't have any meaninful experience to report.
Thanks John - I guess that will do the trick.