I too have never heard of DABLE, and I have to agree that it makes no sense. For starters, using a landmark as a check of maintenance of Direction will not work in a strong crosswind - something that I have noticed that many instructors have totally failed to see through, although it is fun to play along with them on an FI refresher course. Also, why bother to look at the slip ball? Yes I know that the idea is to maintain balanced flight, but if the correct attitude is being maintained and the heading remains constant, then the slip ball cannot be anywhere other than in the middle. Finally, it would appear that this scan is confined to climbing/descending only, so what scan is the student taught for S&L and turning? Sorry Twizzle, but your man does not sound like an A1 to me.
Where I work at the moment, plus all the other places both military and civilian where I have been previously, the Lookout-Attitude-Instruments scan is taught. It is used for all visual flying, not just climbing and descending.
Regarding lookout in a climb, although the weave is the preferred method, lowering the nose briefly (without attempting to maintain airspeed or to retrim), is taught as an option during a prolongued climb on a cross-country.
BEagle, when were you on Gnats? I did my advanced flying training at Valley in the mid 60s on them.