Add Proxmox VE 3.1-21 Node to Cluster with 2.2-31 nodes

Hello,
i have a clustered installation with:

• Three proxmox 2.2-31/e94e95e9 nodes
• Storage for VMs on iSCSI
• Storage for VMs on NFS

For several reasons, i need to do mainteinance and i would like to add more nodes to the cluster to move VMs.
Is possible to add nodes with a more recent Proxmox version (3.1-21/93bf03d4) to the cluster of 2.2-31 nodes?

I would like to:

1. Add two more nodes to the cluster
2. Migrate VMs to these new nodes
3. Do HW mainteinance to the old servers
4. Upgrade Proxmox from 2.2 to 3.1

Many thanks
Bruno