Hi there.
Just a quick update to let you know the results of my experimentation.
The Unity ARKit plug-in provides a load of scripts that make setting up basic AR pretty easy. Trying to set something up using PlayMaker may actually end up being more work!
I have a few, basic actions made (to detect hits, and such) but they depend on the ARKit scripts all being set-up correctly.
I'll keep working and will share any actions I end up writing!