Iron Vault has support for Creaturs by using the related Oracle Entity, which can be rolled either through the Sidebar or through the Generate an entity command. You'll be given the option to save the results into a new file, which will include a Markdown table with all the roll results. Rolling this oracle group will also record the results in your journal.
Besides this, there is no additional support specific to creatures. You are free to organize these entities however you want, including having multiple creatures in a single file (although we recommend doing 1-entity, 1-file as a general rule).
For combat with creatures, you can use Create a progress track to create a combat track, and possibly embed it in the creature's note by using ![[Creature Name|iv-embed]].