ESXi 5.0 to 5.0 Update 2 - Best practices / backup plan

I'm planning to patch my ESX cluster (2 ESXi 5.0 hosts) to 5.0 Update 2. While there's no DRS activated (only HA), the idea is to vmotion the VM's from one server to the other, leaving one of them at each time with no VMs at all, put it on maintenance mode and remediate the update (already staged).

Since all the datastores are located on a Dell MD3000 DAS, which backup precautions should I take to reduce failure possibilities? I'm already backing up the host configuration for both hosts using PowerCLI, so is it necessary to also backup all the VMs inside the DAS? If yes, backing up only the VMDKs is the way to go or should I use a specific tool like vDR, Veem or similar? Are snapshots a safe replacement?