2018 MacBook Pros and imaging

tjhall was correct, the quickadd.pkg needs a product ID for it to work. The "System Image Utility" trick is a good tip for testing. Thanks. After digging for awhile it turns out it's not that hard to add a product ID to an existing pkg. Using Terminal here is a quick summary...

For the following commands below, I ran the commands from the same directory that my content was in so paths were not required.

Generate a distribution.xml with the below command:
productbuild --synthesize --package okit-admin-jamf-pro-join-2018-05-07-10.4.0.pkg distribution.xml

Edit the generated distribution.xml and add the below line (edited for your needs, I don't think it really matters what it says here) above the last line </installer-gui-script> in the xml:

<product id="ca.okit.quickadd" version="1.0"/>

Create a new pkg with the distribution.xml:

productbuild --distribution distribution.xml --package-path okit-admin-jamf-pro-join-2018-05-07-10.4.0.pkg okit-admin-jamf-pro-join-2018-05-07-10.4.0-new.pkg

Test in System Image Utility and installing it on a workstation. Also note, signing wasn't required after all, at least for now.