How does one go about finding developer resources for closed applications like Oracle ATG (or really any of the above list)?
I'm employed by an eCommerce vendor myself, so I'm sure I'd have an intuitive understanding of general architecture, but actually understanding the internals of a system as an outsider seems like a difficult proposition.
Until Oracle bought ATG it was basically impossible. But Oracle has made ATG available for download, including documentation, to anyone, without needed a million dollar support agreement. You can't run a production site for free obviously, but at least now you can read the docs, and play with the software locally.
The only real hope of learning it though is to have a company that you work for use ATG, send you to training, and get you coding on it every day.
This is why there is such a huge gap between the demand and supply of this skill set currently.
They're cutting some of the fat off, but they just dropped 1 billion dollars on the ATG product and are pushing it pretty hard and Oracle doesn't have anything that's a real competitor in the space. It'll get renamed as Siebel Commerce or something, but it's not going anywhere for a long time...