The users will have accounts on our WordPress MU installation and would be small businesses. We would customize the theme and offer it as part of our premium service – allowing them to use the customized theme and its features on their sites (blogs)..
The FAQ seems to support that use in this manner is suitable, but I wanted to make sure:
"If you will be customizing the theme and selling it to a client or using it in a premium service project, you need the developer license."