Make sure your Hyper-V is SP1 patched to get dynamic memory features.
Use Centos 6.1 rather than 5.7, as it's essentially RHEL6. 6.2 is out, but some are reporting issues with hyper-v.
It's supported in Hyper-V with Linux Integration Services 3.2, which you can grab from
Microsoft site
End result should be working system without too much effort.
Is it officially supported? Most likely not, since Centos isn't listed as supported platform, so you're stuck with community support.
But you shouldn't have too much trouble with it either, unless you start modifying the system too much.