Whether it works with a single AA flashlight depends on many factors, but the sad answer is likely no.

With an incandescent bulb, polarity is rarely an issue, and the light should still work, unless the battery connections are such that they will not make positive contact with a reversed battery (which is unlikely).

With an LED, there's a chance that there's some minor circuit protection, but in likelihood there's not much, if any. Reversing the battery would simply forward-bias the LED (as with a normal diode; most LEDs must be reverse biased to light up IIRC), and the battery would simply drain.

Both cases also require the switch to be on, of course.