there's also another question though - were there any Picts in Orkney when the Vikings settled?
some of the sagas say that Orkney was deserted when the Vikings arrived, which would certainly account for the complete lack of Pictish placenames. I really don't buy the annihilation theory, and to be honest I'm not sure about the integration theory either. but if the natives left before the Vikings arrived (or soon after) then we wouldn't expect to see Pictish names in Orkney. Pictish artefacts found in Norse settlements could of course be plunder or traded goods from other sites
Cheers
Andy