Mostly everyone does this, and it is very plausible in-RP that it can be done, especially with systems under the close scrutiny of the IMG and the CR, who, yes, do help each other out with various things, including pirate activity.
It'd be a funny fact if the IMG would not constantly monitor traffic through the Tau 39 and assorted Tau jumpholes, just like the Colonials do, in-RP, because A) It is not a difficult feat to do, and requires little resources, and B) It is very much needed.
The players list is simply a means of achieving that kind of roleplay in reality. Now, I don't see why people should speak like this:
"Ahah! Through our clever use of stationary probes which monitor jumphole traffic, I have concluded that you are located in this system, so come out, because I know you are here!"
It'd be very awesome if we had near a thousand players on the server and the roles of reconnaissance and stationary guard checkpoints could actually be done, but I think it'd be a bit too much to ask of people who come here to have fun, and not work work work.
Though, truthfully, there are cases when people on the server use this kind of RP when it comes to basically any other system which, in some cases, like say, an independent pirate "knowing" there's currently a ship passing through system X, and monitoring his travels in real time, but there's no problem with using one's contacts to get information about spatial traffic, especially considering that, in-RP, you cannot traverse the whole length of Sirius in a couple of hours, like you can do in "reality".
Just remember Trent's neural log and his two week trip to Manhattan aboard the rescue ship.
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<span style="color:#000000">All morons hate it when you call them a moron.