tomfoolry,
Just a hunch, but is the output of scp being written to STDERR and not STDOUT?

Update: Apparently not. I tried:
scp user@host:/path/to/file . >foo 2>bar
Without capturing the progress bar in either file. Incidently, you can turn the progress bar off with the -q option. I wasn't expecting this to produce a nice plain text output given the nature of how the progress bar works, but I would have at least expected something - odd.

Update 2: You might still be able to do what you want without the progress bar. If you disable the progress bar with -q but enable verosity with -v, then all the same information that is in -q can be read on STDERR. Incidently, scp exits with 0 on success and >0 on error.