The plug-ins were built with essentially the same SDK that's available on the website. There have been some speed optimizations, but no new features.
HDR works, use the Cmaxwell::setEnvironmentLayer() function to set the layers and Cmaxwell:enableEnvironment() to turn on the image based environment.
Multilight should also work, enable it like this:
byte val = 1;
scene->setRenderParameter("USE MULTILIGHT", sizeof(val), &val);
If that doesn't do it (it works here) you can also enable it in the command line when you run mxcl, but I don't know if this is an option for you.
I can't offer "official" support, but if you have any other SDK questions I'll try to answer.