Note: this list is generated by looking for the string for this theme hook, so it may include some references that are not actually using this theme hook.

backdrop_common_theme in core/includes/common.inc
Provides theme registration for themes across .inc files.
file_manage_form in core/modules/file/file.pages.inc
Page callback: Form constructor for the file manage form.
node_form in core/modules/node/node.pages.inc
Form constructor for the node add/edit form.
node_type_form in core/modules/node/node.types.inc
Form constructor for the node type editing form.
redirect_field_attach_form in core/modules/redirect/redirect.module
Implements hook_field_attach_form().
system_element_info in core/modules/system/system.module
Implements hook_element_info().
taxonomy_form_term in core/modules/taxonomy/taxonomy.admin.inc
Form function for the term edit form.
taxonomy_form_vocabulary in core/modules/taxonomy/taxonomy.admin.inc
Form builder for the vocabulary editing form.
_form_test_vertical_tabs_form in core/modules/simpletest/tests/form_test.module
Tests functionality of vertical tabs.