Did boot a PowerMac G5 with FreeBSD-12.0-BETA4-powerpc-powerpc64-dvd1.iso and went through installer using an automatic full disk UFS filesystem and the Apple partition type. On first boot the system seems to find the boot block and begins to boot but then halts with a prompt looking for the root filesystem. Also provides a list of filesystems found including the DVD still in the unit but entering things like ufs:/dev/ada0s2 just result in unrecognized filesystem type.
Let's close this as RC2 is out now and I can not reproduce this on the Apple PowerMac G5 "quad" unit.