First of all, beware using OpenFiler with ESX: http://kb.vmware.com/kb/1026596
That said, if you wish to go ahead, you could expose multiple <2TB iSCSI LUNs from OpenFiler to ESX and then grow them together as multiple extents of one VMFS filesystem. There shouldn't be an issue of one extent going down since they're all exposed from the same storage. But then you'd have to create multiple VMDKs on top of that because they are also limited to 2TB, and then Windows would have to be responsible for assembling them into a single volume.
So, perhaps it would be easier in this case to skip the VMware storage layer and expose iSCSI directly to the guest VM using the Windows iSCSI initiator? Windows 2003 SP1 and above should be able to handle LUNs larger than 2TB without fancy workarounds. This should also steer you clear of the ESX+OpenFiler problems listed in the KB article above.