A updated build of vSphere was released tonight. Although not listed in the release notes, this build proved very important. vSphere 5.1 is now supported with View 5.1.x. Please be aware however, you must be using the new build of vSphere that was released tonight. If you already have vSphere 5.1 installed and are ready to install View, you can just apply patch ESXi510-201210001 to your installation.
For all the details you can refer to this KB article.
Additionally, the VMware Product Interoperability Matrix has already been updated to reflect the new build of ESXi and vCenter required for View 5.1.x.