I feel like this is a really basic question, but I can't seem to find an answer for it.
I'm working on a project that would have content hidden on the page, but would be visible through a js interaction (such as an overlay, or a slide show, etc).
The content would contain transcribed information for an accompanying image, so it's important to me that the GSA index these divs as well as all of the visible page content.
My gut tells me it should, as I don't think the GSA takes css into account, although I wanted to make sure before proceeding any further with the project.
The GSA does in fact index hidden elements on the page. I have experienced this first hand on a few implementations where there was hidden debug information on the page that was ending up in the index and having an adverse affect on relevancy.
The only way to keep the appliance from indexing content on a page is to use the googleon/googleoff tags (http://perishablepress.com/tell-google-to-not-index-certain-parts-of-your-page/)
So for your use case you are definitely covered and the extra information would be indexed.