How can I render my output in a series of DIVs rather than an "item_list"?
As far I understood you want render the following code in multiple &lt;divs&gt;.

$page_array['photo_gallery_arguments'] = array(
  '#title' =&gt; t('All photos from ever'),
  '#items' =&gt; $items,
  // Theme hook with suggestion.  
  '#theme' =&gt; 'item_list',
  '#type' =&gt; 'div',
);


Replace it with the following code.

   foreach($items as $item_key =&gt; $item) {
     $page_array['photo_gallery_arguments'][$item_key] = array(
       '#type' =&gt; 'container',
       '#attributes' =&gt; array(
         'class' =&gt; array(
           'my-class-' . $item_key,
         ),
       ),
     );

     $page_array['photo_gallery_arguments'][$item_key]['content'] = array(
       '#type' =&gt; 'markup',
       '#markup' =&gt; $item,
     );
   }


Or use the following code.

   foreach($items as $item_key =&gt; $item){
     $page_array['photo_gallery_arguments'][$item_key] = array(
       '#type' =&gt; 'markup',
       '#markup' =&gt; '&lt;div class="my-class-"' . $item_key . '&gt;' . $item . '&lt;/div&gt;',
     );
   }


Alternatively, you can use the following code.

   foreach($items as $item_key =&gt; $item){
     $page_array['photo_gallery_arguments'][$item_key] = array(
       '#type' =&gt; 'item',
       '#markup' =&gt; $item,
     );
   }


You can find more information about rendering arrays, and Form API.