Any spectator mode in any type of competitive PvP type game would have to be on delay if they don't want cheating. Say if you were playing a capture the flag battleground. You could have your friend on Vent spectate the game and tell you where the other teams flag carrier is or call out what the other team is doing or where they are located.

People complain a lot about WoW not having this for their PvP arenas and battlegrounds, but the main reason Blizzard doesn't do this is because people would cheat with it if it was real time. They said something along the lines of they didn't want to do the delay thing because it would be a lot of work to program record save everything that happens then replay it at a later time and they just didn't want to do it.