Parallel Caps as a Bipolar (twin polar in combination)
do they actually act as a 2.2uF rather than 4.4uF working as a pair?

In parallel they do act together as as 4.4 μF capacitor. This will halve the 'crossover' frequency, which could have some bad effects.
The most obvious effect is a change in the speaker system's frequency response. The tweeter is now being asked to reproduce sounds one octave lower than normal. Instead of response being rolled off at resonance, it may now get full power producing a sharp peak.
Below resonance the speaker system's impedance will be reduced due to the tweeter's low impedance in this area, increasing load on the amplifier and possibly increasing distortion. With more power going into the tweeter it may blow up at a music level that it could normally handle.
Despite all that you may not notice any effect except by doing a careful listening test or measuring the frequency response. However you might find that some music sounds a bit 'off' compared to playing it through the original speaker. This may be particularly noticeable if you only modified one speaker of a stereo pair.

What happens exactly to reverse current across a cap because you can
couple AC and it passes through and people use polar electrolytics for
that ... maybe they shouldn't.

So long as the waveform is pure AC and ripple current isn't too high an aluminium electrolytic capacitor can handle it fine because there isn't enough time for depolarization to occur. However in medium or high level circuits there could be measurable (if not audible) distortion. In this article published in Electronics World December 2002, A 1 μF electrolytic capacitor produced significant distortion when 2 V at 1 kHz was applied across it. In a high power speaker system the voltage could be 10 times higher than that - enough for the distortion to be audibly noticeable and perhaps causing degradation of the capacitor due to excessive ripple current