Uh. I don’t think this has anything to do with the Tumblr website update for iPad. But I just noticed that if you use the site with a browser like iCab, you can actually upload photos or other files from its built-in, Dropbox-friendly downloads section. As far as I can tell, this seems to work with lots of sites that let you upload files. Fantastic.
Don’t think you’re off the hook for a full iPad app, Tumblr. This will help. For now.