Rogue's Perspective
This matchup can be very easy or very difficult. It all comes down to the skill and playstyle of your opponents. There are the Disc Priest/Lock teams who play very aggressively and there are those who play very defensively.

Aggressive play is basically trademarked by them rushing in on mounts at your Shaman and Dotting him up while trying desperately to make him waste his trinket on a Fear. After that they more or less just burn/drain spam him while ignoring the Rogue. If they are able to keep up the pressure, they can win because the Shaman has to LOS to avoid the pressure and that opens up opportunities to Mind Control/Fear on me. Once he's out of Mana, the combined DoTs of the two players will kill him, water shield or not. This doesn't seem so dangerous, but you will be scared once you come up against a team that is good at this. The General tactic here is to basically control the two players as best you can by target swapping quite a lot and shiving them so that your Shaman can run.

The defensive play is trademarked by careful Dotting of the Shaman while waiting for the Rogue to show up. I prefer to come up against teams like this, because they have little to no chance of winning unless I fail to Kick like twenty Fears per minute. The Shaman just avoids burns as best he can with Rank 1 Earth Shock and Grounding Totem. If I, as a Rogue, keep enough pressure on the Warlock so that the Priest has to focus on healing him, the Shaman doesn't have to worry about eating a Fear and Mana Burns without being able to do anything. If he does get Feared, a quick Shadowstep to the Priest to interrupt the Mana Burns works. Communication is vital. Keep Expose Armor up and you will win.