Adaptec have posted updated drivers for use with ESX4 which can be here.
The upgrades for all previous versions of ESX are RPM files but the upgrade for ESX4 is a .vib file. vmware-esx-drivers-scsi-aacraid-400.1.1.5.2465-1.0.4.2465.x86_64.vib
I'm guessing this is installed with the esxcfg-module --add command but I can't find any documentation on it and Adaptec haven't updated any of their installation manuals.
Thanks for any help!