The short answer is 'no' the RoleEnvironment does not support getting all the configuration setting values.
A slightly longer answer is that getting configuration settings from the role environment in the current implementation is done through a call to native code. The separation of Windows Azure Application from Windows Azure Configuration and the ability to swap settings on a running application is at the root of this somehow. This is done inside of msshrtmi.dll (which should mean something like Microsoft Shared Runtime Managed Interop). This is the only reference Microsoft.WindowsAzure.ServiceRuntime.dll has apart from standard references to .NET.
Here is the method call to native code (I have not gone further than this):
[MethodImpl(MethodImplOptions.Unmanaged, MethodCodeType=MethodCodeType.Native), SuppressUnmanagedCodeSecurity, DllImport("", EntryPoint="", CallingConvention=CallingConvention.StdCall, SetLastError=true)]
internal static extern unsafe int modopt(IsLong) modopt(CallConvStdcall) RdGetApplicationConfigurationSetting(ushort modopt(IsConst), ushort*);