Well, we need a second person with a G5, someone here?
I do not suppose that you burned 2 DVDs wrong.
Try it with a bug report, here is one still open:
	
	
		
			
			
				
				
				
					
						
							 
						
					
					bugs.freebsd.org
				
 
			 
		 
	 
Also you can subscribe to the ppc-mailing-list  :
	
--- edit: -
1 person detected  on G5 (running 12.0, so should be possible ) :
	
	
		
			
				
			
			
				
				I'm running on a power mac g5 trying to get a GUI running, KDE, XFCE, Compiz-Fusion, MATE, whatever.  I keep running into an error when building gstreamer1-plugins-bad:  In file included from rtpreceiver.c:33: rtpreceiver.h:38: error: redefinition of typedef 'GstWebRTCRTPReceiver'...
				
					
						
							 
						
					
					forums.freebsd.org
				
 
			 
		 
	 
Tier 2 means something like this :
I remember on my G4-install  there was no Pkg-repo for ppc( had to compile everything through ports or manually  which was slow but worked )
It was a successful experience, I targeted in running a tape drive from that machine and it worked. And FreeBSD was the absolutely only system installable  on my G4 - all other (except Mac OS of course ) failed. So no reason to give up with FreeBSD for you if you have special reason to install FreeBSD on your G5 . Good Luck !
--
some details from my memory:
G4 FreeBSD-CD booted until 
Stage Three , then I typed:
unload
and then :
boot-conf ( install starts then)
or :
load /boot/kernel/kernel
an then :
boot
--
you could try to clone the install-iso to a hard disk instead of dvd and boot from there (firewire or internal partition)