It shouldn't have any effect on the server and it also shouldn't make you lag just by being close to him. It would definitely add to his latency but in some cases it can actually improve a player's route to the server. I only have a problem with players using proxies etc. if they are trying to evade a ban.
ACE usually kicks players if their connection problems get bad enough. Still, we can sometime see players warping around from time to time and it's not great for game play but this is usually just temporary and can happen to anyone so I just try to be tolerant of it. Most of the time they are back to normal in a few minutes to an hour or so.