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...
Note: what I'm about to say has zero technical base since uh, you know, I don't care about technicality or purity, we're talking about pure business direction here.
I'm unsure regarding Scala since a few articles have risen regarding getting burned by Scala (Yammer) or plainly suggested that Scala may not be it (David Pollack, one of the Scala celebrities).
Having said that, knowing Java developers, most (not all) of them would definitely flock to either Scala or Groovy instead of LISP. Have you heard anything about Groovy lately? Yep, nada, cricket. The cool kids (Yammer, Twitter) are using Scala (to some extend) so there you go.
Clojure on the other hand has that "LISP" tales behind it (LISP programmers are like gods or something like that) and it runs on Java so that gives people some kind of hope and smile on their face or something.
I don't know if either would be in high-demand but you may want to look around and do a bare minimum, out of the thin-air, lots of grain of salt type of assumption: