Firstly, if you're using NPC's as a guide - (which we shouldn't because quite frankly people use NPC's when it supports their point of view and ignore them when it doesn't) - then looking at the inhabitants of alaska... Order, Navy and BHG.... its easily conceivable that with all those people having access to the Codes to the gate that that information would not be able to be kept secret. Added to that, with the known Corruption of the LPI, who also it seems from reading on here, have access to the gate, then its also concievable that they would sell that information.
In fact, thats completly how i would justify it - I bribed someone to get the codes, or i beat up a bounty hunter to get them, or i shot down and captured a navy pilot who had them in his wallet - my point is there are all kinds of good Role Play reasons why a shady nefarious character might be able to find access to this gate......
Now added to that if you say that the Order has access to it? well... that basically ensures that the Corsairs do as well, as well as their friends etc etc etc......
As for Alaska being secret - Xing has a point in terms of RP. But i see it a little differently, perhaps Alaska might be secret for lawfuls and agencies that stay within the boundaries of the Liberty Laws... but for unlawfuls? who couldn't give a hoot what the Liberty rules say? Again.. they have access to the jumpholes on the other side of the system, the Corsairs and outcasts have extensive reach both militarily and in terms of knowledge of jumpholes (lets face it they need them to survive) - and again, particularly in terms of the Corsairs, their allies the Order are sitting on those jumpholes. As such, to me, its simply inconceivable that these groups in particular would have no knowledge of Alaska.
The way I've always seen it - is that the system IS open in the mod - and it's known. I've always felt it is the responsibility of the Liberty players to enforce that Zone 21 rule, NOT the responsibility of the unlawfuls to self-police in this case (especially when there are ample RP reasons for them to be able to get there as i have stated). I constantly hear about liberty being a "cap ship" haven, but i am yet to see any kind of regular guard sitting at the gap in the minefield. - was this to be a regular occurance, were smugglers, traders etc etc to encounter regular resistance here, i gaurentee you they would double think coming through Alaska.
Its not the unlawfuls problem that the Liberty lawfuls cant always watch it. They aren't there to help them! Its an unlawfuls RP to take full advantage of any weakness or gap in law enforcement to their advantage - If liberty cannot protect her own borders effectively that is their own problem the way i see it.