We have a .Net library that accesses some custom hardware via a USB port. I've read that Silverlight contains a subset of the .Net runtime. So, my question is, would this subset be sufficient for the .Net library to function?
YES YOU COULD
an update only for people like me that founds this question, here the answer:
No, you cannot use a .NET library that accesses a USB port from inside Silverlight.
The closest you can get is an SL4 Out-of-browser app with elevated privs which can use COM components.
来源：https://stackoverflow.com/questions/2252683/can-silverlight-access-a-net-library-that-accesses-a-usb-port