Yes it is accessible to some extent. Some of the mozilla screen readers stop / break at certain points - I'm not sure why. I think it may depend on the type of graphic insert that is used. Readers see all of the text formated paragraphs. The reader also recognizes the floating text descriptions.
One of the work-arounds I've found is to scroll the Spark Page to the area you want to read, then invoke the reader again.
As long as there are descriptive text elements used with the slides, they (in my page layouts) are accessible.
Thank you for your reply. When I insert images such as a graphic, I do not see a way to include an alternative tag description. Is there a way to add an alternative description tag for images that I include in a Spark?