I am participating in the ZCB 6.5 BETA Programm that provides support for BES 5.0 and BES Express 5.0. I was able to setup a testenvironment today. Our testsetup is:
Zimbraserver: ZCS 6.0.5 NE on Redhat, x86_64
BES Server: VM with 2GB RAM, 50GB HD, Windows 2003 R2 (I know, its not offically supported) Standard, 32bit
BES: BES Express 5.0.2
To make a long story short: it works :-)
I could successfully activate my BB on the first try. Mail, Calendar and Contact sync works in both directions. GAL search works. Within the next days we will put some users on the testserver to see how the server performs under some load.
The installation is tricky (not to say a nightmare). Follow the installation guideline closely. For some reason, the BES 5 needs an AD (to authenticate the admin user). But later you can/should switch to the build in "Blackberry Authentication Service" which seems to be kind of local authentication Database.
Very good work Zimbra!