Some pages are just lists of married people or lists of baptisms. Only their names, no other info. Do these get indexed somehow or do I just mark it unreadable?
It is very difficult to answer a question without seeing the batch. To share the batch, you should use the 3rd icon from the right and provide either the batch link or the batch code. Or you can copy and paste the title of the project with the batch code that follows.
However, the project instructions say
So, I would index all of the marriage and baptisms on those pages.
You never mark an image unreadable, unless it is smeared or torn, or unreadable due to something like bad photography. You could possibly mark an image as No, No Extractable Data, but if there is data to index, then you would not want to do that either.