Can I use the app offline?

Yes, the app is able to be used offline.

Many of the features of Rookie Me Play require users to be online, therefore using the app offline will limit the functionality available.

Features available offline:

Run through an event which has previously been created and set up.
View all areas in read-only mode.
Data is saved locally until you are next online. Note: You will need to manually back up the data once connection is restored.

Refer to the following article for further details of the above