Where to put hidden fields when displaying entities properties in a table?
When you are iterating over the collection of people, it probably does make sense to keep the hidden fields within the loop. I would try to keep them grouped together in that first td, with a hidden field per line, so that they are easily noticeable when scanning the source.

If I weren't iterating (meaning that I was using some field at the top of my model, not in an array), I generally stuff my hidden inputs immediately following the opening  tag.

When iterating, within the td, a hidden element should have no effect on the rendering. You might consider wrapping them in a  or  with display:none applied. I believe there are some (older) browsers that will render white space if you have line breaks between your hidden inputs.