HP has now updated the advisory that describes the issue and published an updated firmware that fixes the VLAN handling problems with ESXi 5.0 if it is used together with the be2net driver 4.0.355.1.
Be sure that you read the release notes of the firmware! It looks like it is an emergency/workaround release that leaves many issues unresolved. A firmware version that you can really trust for production will probably be available mid-November.
Update (2012-04-16): Please refer to my HP & VMware links page to find the download for the latest version of the firmware.