I’m not sure whether this represents a Packer flakiness with keyboard timing, or whether Haiku nightly itself is flakey, but for some reason when I navigate to the live installer, VirtualBox often shows a boot failure rather than the installer.
Update
I believe this to be more of a user timing issue than any problem with the Haiku installer, so I am adding more time between keyboard navigation to complete the install GUI in a relatively reliable, automated fashion.