As far as I know, WinRunner has never been outfitted to run .Net This was one of the reasons that Mercury brought out QTP. At that time, WinRunner was placed in a mode where only updates were basic changes and no new functionality would be added. Recently, I've heard that maybe they will up-grade WR, but until I see it, I don't believe it.
That being said, many of the objects in .Net are the same or similar to non-.net and therefore can be automated with WR. Only the .Net specific objects can not be.
WinRunner does not recognize .NET objects in Windows applications. I read some time ago that there was a third party tool available that added .NET support for WinRunner but I haven't been able to locate that tool. Perhaps it was vaporware.