I had a quick look and all the manual says is that Raildriver is automatically recognised and nothing needs to be done.
On another page, it says that Zusi does not recognise devices plugged in while Zusi is running. But you sure started Zusi again at least once after you plugged in Raildriver.
Do you have multiple devices collected? There is a whole set of pages devoted to this case, but it seems to address those with a complex cab.
Maybe post a question when in the English Zusi forum? Those who own Raildriver will have made their experiences over the past days that may well deviate from what the manual says.

Not that I blame Carsten for that but when I read "you should not need to do anything, something in me frowns every time".
You could dump promising subsubsections into Google translator and when that does not result in something anyone can understand, point me at it.