Nothing official but this doesn't sound like a good idea.
I would suggest working the other way though as Windows 7 as 7 has more potential for backward compatibility than older versions being able to handle new changes to the OS.
I create all my runtimes in Windows 7... I have done for quite some time (including in Windows 7 pre-release versions)
I have no problem with it being used under Windows XP or vista (both 32 / 64 bit versions)
It does not matter which version of windows you use to build the runtime, all it does is copy a selection of files from the FMI Runtime Resources folder and make some small edits to one or two of those files during the build process, to store binding information etc.
The output will be the same..
Like you, I also develop on a mac these days.. less crashing and a refined interface.. such as searching scripts / layouts is much quicker and hides any irrelevant folders (unlike windows)
P.S Make sure you grab the new runtime resources from the FMI downloads section, which include the C++ files for V11.