As written in a previous post the current version of Veeam Backup (5.o.2) works also with vSphere 5, due to the compatibility of most of the vStorage API for backup. But to be honest there is some issue, like for example in the usage of the SAN transport mode.
Veeam has publish a post on his blog, to announche the release of a hotfix on 20 October, 2011, to FULLY support vSphere 5. One of the main issues with Veeam Backup & Replication 5.0.2 was that it didn’t work for all processing modes with VMSF5 (just like every other vendor at the time of this writing). A processing mode popular with our customers is direct SAN access utilizing the vStorage API for Data Protection (VADP).
This hotfix is not available on the download page because it’s only available through Veeam support. Of course, Veeam Backup & Replication v6 will have full support of vSphere 5 when it’s released later this year.