I've never tried this, but a search turned up vxWorks' iolib, containing the function ioGlobalStdSet, which should let you redirect standard output to a file that you've opened:
http://www.fys.uio.no/studier/kurs/f...ioGlobalStdSet
You likely won't get the early boot-up messages that go to console as your code won't have been loaded at that point to make this redirection, but if you are just looking to log your "printf" and other stdout-based logging output, this hopefully will do what you need. If you try it, let us know if it works.