I don't think that this is considered removable media, in the same was as CD/DVD or Floppy drive, but would probably be considered in the same way as the internal hard drives.
You can check this by editing the scan settings, Report file, check the generate report and also click the OK files that will show what has been scanned. Also simply looking at the scan results window on completion of the scan would show the number of files scanned, the quantity of data, etc. etc.