As far as I can tell, I doubt it. Xur is given leave to be in the Tower due to the Consensus more or less allowing it (but I don't think they have any idea how he gets there). The Reef is the Queen's territory, so Xur might not be very welcomed there. Also, the House of Wolves is DLC. That would mean Xur wouldn't be accessible to people some weeks if he showed up at the Reef. None of this is official, by the way, [b]just my speculation.[/b]