Security is all about layers. Just relying on single DMZ technology (or any technology) for security is going to be problematic. No two networks are the same and so are there security requirements?
If you place your LB in the DMZ, then what ever is providing your DMZ will also have to bear this load. What is your DMZ doing? packet filtering, l7 inspection, IDS etc etc, or all of those?
What are you trying to protect? and what are you trying to protect it from? What are you
traffic loads? If your maxing out a gigabit link, then you'll need lots of extra infrastructure to deal with that traffic. This infrastructure with have to be fault tolerant.
Why not harden you operating system, apply the correct host based firewall rules, and some basic filtering on your edge router.
Stateful firewalls have limits too, and it's another piece of infrastructure to load balance , monitor and maintain. (and potentially have security problems).
Security is a process. Just implementing a dmz won't really fix anything unless you actually know what your trying to protect and why.
You can keep adding layers, but your adding complexity, reducing complexity is sometime more secure, so it's a real trade off.
I've seen many networks with a plethora expensive network security devices and programs, and when you ask if they take regular offline database backups, they come up blank.
This answer probably posed more questions than answers, but it's an short question with a very long answer.
Any one who responds with 'just install a firewall' , probably shouldn't be answering it all!