Yes. I am running RC15 and have the documentation for the gpio module v1.0
I am now beginning to think that I may have a duff board (or, less likely) two duff switches, as the pi-mote will also not work on Linux with well publicised Python software. I have ordered another pi-mote board from a different supplier (Farnell CPC, who are usually good).
I do get a green LED lit on Linux as well as the red one I get on RISCOS, but I have not seen any documentation about what the LEDs are trying to say. Perhaps, something to do with the fact that the Linux is running an original Pi 1B, whereas the RISCOS is on a B+.
Any further help about GPIO on RISCOS BBC Basic would still be useful.