Are there any benefits to using a Distributed vSwitch for iSCSI?

Not the answer you want to hear but we've had so many problems with distributed switches, even with 4.1, that we don't use them at all, let alone for iSCSI. As for benefits, none leap to mind.

I really think it depends on your environment and the number of host you have to manage. One of the biggest benefits to vDS is the ability to centrally manage the network configuration of all of the host in your environment. With a standard switch you would have to make that change manually on each individual host. Another benefit is the elimination of configuring an etherchannel on your physical switch as you can use the load based teaming features available in vDS. That's just a couple that come to mind. Hope this helps.