These are some test photos that I uploaded to see how a “photo set” might work.
Would this work for a photography portfolio site? I don’t see how it could. Tumblr actually goes a very good job of showing the photos. Well, I don’t like the way they organize the thumbnails very well. But when you click a thumbnail to see the photo full size, that’s great. About as good as Google+.
The problem is — you can only have 10 photos in a photo set! And as far as I can tell there’s no option on Tumblr for having private galleries.