View 5 is supported on vCenter 4.1 update 1 and 2 and vSphere 4.1 update 1 and 2. I would upgrade the ESX 3 host to at least 4.1 update1, then go in and upgrade the View 5 environment, once that is completed you can upgrade to vSphere 5 whenever you choose.
http://partnerweb.vmware.com/comp_guide2/sim/interop_matrix.php?
