Yep. You'd have to either know what was on the whitelist or do some kind of bruteforce. Wouldn't be very hard, although I think this stuff is logged centrally in organisations as data-paranoid as the NHS so some random box hotplugging thousands of different peripherals every minute would attract attention pretty quickly, you'd hope.
When I was (working) at the hospital most of the records were still on good old hard-to-steal paper. Still are IIRC, the governments plan to IT-ize it all was fucked up by the vendors in exactly the way you'd imagine.
