Stucco cracking/polymer additives/AAC
Congrats on your choice of materials, FYI. AAC is great stuff, totally appropriate for your climate. 

Applying stucco over AAC isn't a fundamentally different process than applying it over mortared block or brick, so if most stuccoed masonry buildings in your area aren't full of cracks, you should feel more at ease. The only real difference that AAC may present a smoother surface, which could lead to worse bonding compared to a rougher brick or block. That's probably why the instructions call for a polymer-modified plaster; the polymer additives make it stickier, to promote superior bonding. The traditional way to promote bonding is with metal lath. However I honestly wouldn't recommend this in your climate since moisture will eventually rust it and the stucco will come off (rusting metal expands, cracking the stucco).

You have three options: obtain a polymer additive and instruct the stucco crew to add it to their stucco mix; hire someone to mechanically roughen up the outer wall surface before the stucco crew arrives; or let them do their normal thing and hope for the best (it will probably be fine).