During the last patch cycle VMware made VMware View 5.1 and vSphere 5.1 compatible with each other.
For VMware vSphere 5.1 to support View 5.1 you need to do download a patch for ESXi 5.1 or an up to date ESXi 5.1 ISO image.
To download the ISO:
- Navigate to the vSphere Download Center.
- Click View Download for the VMware ESXi 5.1.0 Installable for your version of ESXi.
- On the Product Downloads tab, download VMware-VMvisor-Installer-201210001-838463.x86_64.iso.
To download the patch, download ESXi510-201210001 from the Patch Download Center.
Just like with all the other updates: Before you update, make sure all the other components are compatible as well. For example back-up solutions and anti-malware are not always compatible with the most recent versions. Check the documentation before you do the upgrade.