Is there a quick/easy way to add photos I take with my iPhone directly to my zen photo gallery?

Is there an app for that?

Try this one: http://www.zenphoto.org/news/zenphoto-ios-app/

Gave that a try yesterday, not working.

Followed instructions here: http://zenphoto-app.tumblr.com/

You downloaded the app as well?
https://itunes.apple.com/us/app/zenphoto/id968674016?mt=8

As far as I understand that iOS app requires also a plugin of the same name. If you got trouble with it you need to ask its developer. Not sure if he reads here regulary. Here is the GitHub repository for the plugin: https://github.com/djmonta/zenphoto-iOS-plugin