So, after much debate, and a lot of searching, I couldn't turn up a reliable way to install a binary of the latest version of the zabbix agent on OSX (OS X) Yosemite 10.10.3. The following is the quick approach I took and it works beautifully.
First, install xcode. I know, groans abound, but it's required so just do it unless you feel like you want to trust my binaries. Secondly, grab the zabbix source code, it's free and relatively small.
Next, follow the sequence of steps exactly, it is easy, fast and relatively pain-free. From a shell as an administrative user:
Install command-line tools:
user:Downloads user$ xcode-select --install
Untar/uncompress the latest tarball (2.4.5)
user:Downloads user$ tar -zxvpf zabbix-2.4.5.tar.gz
Switch to the tarball directory
user:~ user$ cd zabbix-2.4.5
Run the configure script with the --enable-agent switch
user:zabbix-2.4.5 user$ ./configure --enable-agent
Make the executable
user:zabbix-2.4.5 user$ make
Make the necessary local directories
user:zabbix-2.4.5 user$ sudo mkdir -p /usr/local/etc /usr/local/sbin
Copy the configuration file to the local etc directory
user:zabbix-2.4.5 user$ sudo cp ./conf/zabbix_agentd.conf /usr/local/etc/
Copy the daemon file to the local sbin directory
user:zabbix-2.4.5 user$ sudo cp ./src/zabbix_agentd /usr/local/sbin
Edit the agent daemon file (beyond the scope of this document)
user:zabbix-2.4.5 user$ vi /usr/local/etc/zabbix_agentd.conf
Start the agent, and enjoy!
user:zabbix-2.4.5 user$ /usr/local/sbin/zabbix_agentd
I'm working on a clean way to install this as a system daemon and should have that done very soon, as well as a script that automates the entire process, save for the XCode installation. There is also a 'make install' target, I just wasn't sure what that was going to do, so I'd rather do it manually for the time being. I'll update this space as I have time soon!