Documentation for ZS is scattered somewhat. There are a lot of how-tos on the home page and links to docs that ZS users wrote, but nothing cohesive. It seems a Wiki or something similar would be great for documentation.
Sorry, I don’t have the hosting space for one, unless you want to have a Wiki or equivalent on a AMD Geode (like Intel Atom) CPU. It’d be slow-going.
As for AD DNS, I made comments on your later post about how AD has two zones (example.com and _msdcs.example.com) and ZS would need to zone-transfer both of these. The ZS DNS server would also need to permit dynamic DNS changes and somehow have the AD domain controller accept changes coming from it, which doesn’t work the last time I checked. “Bi-directional zone transfers” (for lack of a better phrase) works in AD because AD itself stores the DNS zones instead of using zone files, and AD replicates those between DCs almost seamlessly.
If an admin wanted to publish their AD DNS zone with ZS (and why not? It’d be a good read-only copy and it would avoid exposing the DCs to the internet,) they could do something like what I do with pan-am.ca. I allow transfers from my DCs to ZS and I tell the registrar to refer to the ZS router’s WAN IP as the primary DNS for my domain, but internally I use the DCs as the DNS servers instead. I avoid publishing _msdcs.pan-am.ca though.