Can I serve a hot soup recipe as a chilled soup?
There's no food safety issues here, you don't have to reheat food to make it safe if it was handled properly before it was frozen. Just thaw and serve. 

From a non-safety perspective if it's a soup that's meant to be served hot it will have a very different flavor cold, often being bland. You may want to test it out and tweak the recipe to make sure it tastes good.