Hi,
Unity ads is dealt differently in older versions of Unity 5, it was distributed as a package. We don't support this old way, so If you have a script that works, I would simply hook playmaker to work with that script, sending a message to it and reading public variables for feedback and what not.
Does that make sense?
Also, what staying with an old version of Unity, it's likely going to backfire very fast if you plan on publishing to the app store or google store.
Bye,
Jean