The SPARC/LDoms technology offers two options when setting up ethernet network configurations.
One option is Virtual Networking using vnet, which supports Live Migration, while the performance overhead is minimal since the current LDoms Version 3.2. This is why I would recommend using vnet. Especially when your LDoms are sitting on the same System/VSW and communication stays local. The vnet communication is very fast then and doesn't use the network card at all. Using uperf between 2 small LDoms with 1 core assigned each the throughput reaches more than 7Gb/s on a SPARC T4-1 server.
SR-IOV (Ethernet Virtual Function) is available with new ethernet cards. Older cards don't support this technology. The LDoms Version 3.2 released this month removes the old drawback of LDom panics when the control domains reboots. SR-IOV/VF offers a small performance benefit over vnet, while losing the ability of LDom (Live) Migration. For Apps which require lowest latency the SR-IOV Virtual Functions are the right choice.
What's New in LDoms 3.2