My $.02 ;)
1) This topic surfaces every so often when someone who hasn't seen that Dogfight episode brings it up. By his description Candelaria pulled off an amazing move in real life!
However, whether the Dogfights CGI accurately depicts what happened is totally debatable. I personally wouldn't put too much stock into the CGI depiction.
2) Post stall maneuvers can be done in real life. Most commonly today Aerobatic pilots dazzle air show attenders every year with a repertoire of incredible post stall maneuvers. For instance there are the lomcevak family of maneuvers like the following:
http://www.youtube.com/watch?v=skfprThzUq4&feature=related
http://www.youtube.com/watch?v=6SrF5On5xIk&feature=related
http://www.youtube.com/watch?v=Q1ZxXihk7-0&feature=related
http://www.youtube.com/watch?v=kPM8qveStJ0
http://www.youtube.com/watch?v=L1GVpyHYwtM&feature=related (Sean Tucker)
http://www.youtube.com/watch?v=vpwDrBieXC4&feature=related (40 second mark - Victor Smolin)
http://www.youtube.com/watch?v=cOHSUvGb93E&feature=related (Svetlana Kapanina)
3) Are we able to do post stall maneuvers in AH? Since AH models real world physics the answer of course is yes. Here is an example of a P-51D lomcevak that I call the "flat plate" done in AH that's been discussed in the past (usually in association with Candelaria's maneuver). And yes it's repeatable ;). As with real lomcevak's it's actually a precision maneuver that requires precise controls for entry, control, and exit.
(http://brauncomustangs.org/films/flatplate1.gif)
(http://brauncomustangs.org/films/flatplate3.gif)
4) As to the usefulness of such maneuvers, I would characterize post stall maneuvers like the "flat plate" a last ditch maneuver. Former fighter pilot Andy Bush touched on the concept of "last ditch maneuvers" in a article at SimHQ. Quoting Andy:
Last Ditch Maneuvers. Sometimes nothing you do works. Sometimes the bandit is the Red Baron and nothing will shake him off your tail. Sometimes you are going to have to throw caution to the winds and bet it all on one last attempt to save your skin. This is known as the Last Ditch Maneuver. Last ditch maneuvers are maneuvering techniques that attempt to force an abrupt role reversal through a severe change in closure and/or angle off. In real life, they typically rely on the extreme negative effect on airspeed that high angle of attack (AOA) maneuvers have. But what works in real life may not work in the sim...and too often this is the case. But, as sim flight models become more like the real world, you may find that you can employ these techniques against your opponent.
He further gives examples of the high-g roll underneath or the high-g roll over the top. Here is the link to the last page of the article where the topic is addressed briefly:
http://www.simhq.com/_air/air_023a.html
Tango
412th FS Braunco Mustangs