If your wiki is kept in revision control, a post-commit hook is run every time you commit a change to your repository.
ikiwiki generates the "post-commit hook" once you've uncommented the relevant section (under wrappers) in the ikiwiki.setup.
The generated wrapper is a C program that is designed to safely be made suid if necessary. It's hardcoded to run ikiwiki with the settings specified when you ran --wrapper, and can only be used to update and compile that one checkout into the specified html directory.
Depending on your setup, the post-commit hook might end up getting called by users who have write access to the repository, but not to your wiki checkout and html directory. If so, you can safely make the wrapper suid to a user who can write there (not to root!). You might want to read Security first.