I take it no-one else has found a solution for this?
I have exactly the same issue with a Dell R610, and ESXi 4.1 U1.
The hardware was working fine on a PE 1950 running ESX 4.1, but after being moved to the new server, datastores just get removed after 30 seconds or so.
Spent several hours so far with both Dell and VMware and still looking for a solution....