force block module to load admin panel theme
If what you are asking is if, when you go to admin/build/block, is there a way to make drupal use your admin theme instead of your custom theme, then the answer to that question is no, because it needs your theme to figure out what regions are available and what blocks are in them.  But it will allow you to pick different active themes so you can put different blocks in different regions in different themes if desired once your custom theme has the needed regions and other logic required to work with the block admin pages.