I put the following into a bat file and then execute that from my SQL Server Agent job...

rem RoboCopyErrors.bat

robocopy %*

rem suppress successful robocopy exit statuses, only report genuine errors (bitmask 16 and 8 settings)

set/A errlev="%ERRORLEVEL% & 24"

rem exit batch file with errorlevel so SQL job can succeed or fail appropriately

exit/B %errlev%

I found this here: http://weblogs.sqlteam.com/robv/archive/2010/02/17/61106.aspx