I'm running FreeBSD 6.1 on several servers without problems, and would recommend using 6.1 over 5.4. The 6-series is faster in many regards and just as stable.
I don't use the 6.0 compile of DA, but the 5.4 build with compat5x.
I'm using 6.1 with the 6.x DA compile and it's been working fine. The only real issues from what I remember is getting the licence during the install but that randomly happens with most versions of FreeBSD and having to manually install the webalizer binary (takes about 30 seconds to do) but they may have already been resolved since I installed it. Once it's installed it works flawlessly. Overall I believe its production ready.