"(b) expected" -- bah -- my bad! I said it backwards. I meant: AF-A starts as AF-S and becomes AF-C (if motion detected), as you said several times.
I'll try again. Suppose AF-A is set.
(a) If the SB-600 is NOT mounted, then, if AF-A remains in AF-S, the camera will act like AF area mode S has been selected. If AF-A goes into AF-C, the (manually) selected AF Area mode comes into play.
(b) If the SB-600 IS mounted, then, if AF-A remains in AF-S, the AF area mode acts like (or is?) is AF-S. If AF-A brings up AF-C, then the SB-600 will not provide AF assist (and probably will not bring up any AF area mode, either -- but that should be irrelevant). Anyway, as we said, for SB-600 AF assist, better to just use AF-S focus mode, and drum the shutter. The AF area mode manual setting then becomes irrelevant (as you said).
So, did I finally get it straight?
As I said I would check: with the SB-600 mounted on the D7000, it IS possible to set the camera manually to AF-C.
About using single frame shutter release. You say that in continuous shutter release, the SB-600 recharge rate can be a limiting factor on the frame rate. I have noticed that effect in daylight sports shooting, using the SB-600 for fill, especially when the batteires begin to run down. But in AF assist for theater work, with AF focus mode = S & the SB-600 mounted & set to AF-assist, then if I am trying to shoot continuously, the SB-600 will not assist shot illumination; it only fires when I acquire focus by a half-press, so the SB-600 recharge rate only limits the frequency of focus acqusition, not the frequency of shots. So the SB-600 would not fire during the burst, only at the beginning, when I acquire focus. True?