A folder called upload within the albums folder is an album called upload. So you can directly achieve this by doing what I recommend. Of course the user will have to visit the backend for the upload.
If you want to do this outside of Zenphoto bypassing anything, this would equal FTP upload. You can do that but we cannot really help with that.
> I made a test.php page and stuck it in our active theme.
You really did make a proper static custom theme page? If not doing that it will not work properly. See the example in the official themes like archive.php. Please read the theming tutorial if you haven't yet.