Go into the makefile and disable the a3d support.
But beware, it's going to take a little more than changing the makefile to get it to work on OS X. Since you're on a PPC machine, any of the code that is written in assembly will need to be changed to something that runs on the PPC chip.
Even if you get the paintball2/ref_pbgl binaries to compile and run, you'll still need jitspoe to release a PPC built version of the gamei386.so, and you can port that yourself because it's a closed-source binary. He has no intentions of porting it to OS X until someone buys him a macbook, and there's not really much point in him doing it for PPC since all the new systems are Intels. But if you do manage to pry that source from his claws, let me know; I'm looking for it too.
I think the FreeBSD makefile is broken anyway. This isn't your typical Open Source Project, mostly just a Windows game, using an open source engine, everything useful is still closed source (legitimately due to a different license, code base), and we're just lucky that we've got Linux support.
I'll still keep an eye on this thread and try to answer any questions to have along the way.