Yes. I have done it. We had a solution based on Remoting where each of our stores had a "listener" (service that's called by the client). There's a program in the corporate office's helpdesk that was a "sender" (client). Both initially written in .NET 1.1.
Eventually, we needed to do some updates, and the "sender" was upgraded to 2.0, and it worked just fine with the "listeners".
The key thing isn't the runtime version, it's the interface that's created. We just couldn't change the signature.