In the general case, I think you're right. WinApps seems to use RemoteApp functionality on windows to export just the window you're interested in from the virtualized guest vm to the host, which should behave mostly as a "native" app.

But you were talking about sr-iov, which is a whole different matter. Presumably, the goal is to have LR use that GPU for some of its functions. But LR doesn't support multiple GPUs: it does its computation on the same GPU that handles the output. For that, you need to connect the display to the passed-through GPU. Now, aside from intel, I don't think any mainstream GPU actually supports sr-iov, so you need to pass through the entire gpu to the guest VM (the host wouldn't see it anymore at all). This isn't how RemoteApp works, and I doubt WinApps handles this case.

I remember a project (Looking Glass?) that tried to somehow "bring back" the output to the host machine, but it didn't seem too robust at the time. I haven't followed it, so I have no idea if it's any better now, if it's still alive. If it does, this could possibly work if you had two GPUs (which I happen to have, since my CPU has an integrated GPU). But you'd still get the whole Windows desktop of the VM, not an RDP connection.