You really should login with your S2 account before asking questions about how to use S2 content, the "Demo racer" tag under your nickname complicates things.
Perhaps if you post the name of that team server, we'd see that pretty much everyone behind NAT should be perfectly able to connect, and you could go ask your admin what he's talking about.
I'm very much behind NAT myself, just grabbed the entire server list and got 377 servers, 11 with no reply.
nKPro's release has to be one of the least successful ever, the slogan "Just Drive!" kinda stopped being neat after 50 people posted "how the hell do i start the car?", the massive hype and "most anticipated game" didn't make the 1992 styled UI, dotnet error messages, unlock failures and 30 second ping times better, and the sound is probably the worst of any game trying to make the sound of car engines ever.
Too much work on "photomode" and screenshots, the game itself is clearly still pre-alpha.
Oh, if you try the demo you won't be able to know how fast you're going, or which gear you're in, need to pay for them tasty features.
Even though you can get the LCD/AIM thingie working, this has to be the least intelligent demo restriction ever.
The sound is unbelievably awful, Steinberg wrote code capable of synthesizing sound in very good quality with very low latency thru DirectX - 9 years ago - which even worked on computers from 9 years ago, i seriously cannot understand how you can write a sound engine that has latency "steps", which it seems nkpro is using, ie. 200ms plays the same generated sound for 200ms and then makes a new one, 50ms is still completely horrid.
It even seems Steinbergs SDK is free and without royalties, if i'm not too tired to read legal text.
That sounds really strange, the purpose of NAT is to solve the issue of multiple connection from a single IP, i can't see how your team server can even figure it out in order to reject a connection, never heard of any server or network service that rejects something based on the client using NAT.
Seeing how PNG is completely open source, i guess LFS could write it's own PNG's with relatively little coding. However, i'm with the screenshot-software crowd on this one, IMO there's really no need for a screenshot function in LFS.
Make sure the port you're opening in LFS isn't used by anything else, and that you don't use the same listen port in both LFS and the InSim application.
Yeah the threshold seems absurdly low, but if the purpose is to prevent a DoS attack and with enough clicks the server just stops responding, i guess it's a solid system.
DoS isn't about stealing lots of continous bandwidth in kB/s, it's about generating so much activity that eventually all the server is doing is responding to bogus requests, occupying connection slots.
There's not really anything special to support, using 900 degrees will just result in you having to turn the wheel 900 degrees for the wingman driver to report a full lock-to-lock.