Replay Mod can record packets send by server. Its impossible to force on server to send informations about players outside server-side render distance. If You have access to server files You can change view-distance in server.properties to higher value. < it probably change only terrain range, not players
Edit: my English
As far as I know, it
should also send you information about more players when you inrease the view-distance value, however Minecraft just renders Entities in a radius of 32 blocks (I think).
No guarantees, though :P