This was tested with v3.6 (sorry, didn't test 3.7 since I stick with final releases). Basically I was setting up a minimalistic build server for TFS Service. I installed Windows 8, Team Foundation Server and WiX 3.6. This left me with ONLY .NET 4.5. My first build threw the following error:
C:\Program Files (x86)\MSBuild\Microsoft\WiX\v3.x\wix2010.targets (2339): The "WixAssignCulture" task could not be loaded from the assembly C:\Program Files (x86)\WiX Toolset v3.6\bin\WixTasks.dll. Could not load file or assembly 'Microsoft.Build.Utilities, Version=126.96.36.199, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified. Confirm that the <UsingTask> declaration is correct, that the assembly and all its dependencies are available, and that the task contains a public class that implements Microsoft.Build.Framework.ITask.
I was able to add the .NET 3.5 feature and green up the build. It seems like this should work with only .NET 4.5 installed OR the WiX installer should detect a missing prereq.