G'day Andy,
This is our desired scenario too.
ESX VMFS formatted iSCSI targets being constantly replicated (async is fine) to a DRP DSS (in this case on the GB LAN).
So I think it will be possible, but at this stage the great unknown for us is will it work in a production environment.
The last thing we want is for it to seem to work, but when we revert to the DRP DSS we find corrupted data