The N900 appears to come with a separate layout for the SU-8W in /usr/share/X11/xkb/symbols/nokia_vndr but doesn't use it automatically after enabling the Bluetooth HID. By default it's using the N900 internal keyboard's layout. The Fn key on the SU-8W is not working which suggests it doesn't make the keyboard actually send keypresses of the number keys for example, but the driver has to interpret Fn+Q as 1.