It will be good with a NAS version of Ubuntu server. a Ubuntu version of FreeNAS. The problemet with FreeNAS is that it runs on OpenBSD platform and not Linux. There is no distributions of LINUX with target the NAS marked.

Dynamically Loadable Zones are already in Ubuntu's bind (DNS server) sources but not enabled for the compilation.

This feature is really useful : No bind reloading is required and rules can be simply shared between zones.

If installed manually, it's not hard to activate them (just change --with-dlz-mysql=no to --with-dlz-mysql=yes for mysql), but it needs to be recompiled for each update (And serious administrators update bind at least for each security update ; wich can occur quite often).

The last good point is that databases allow simple backups and synchronisations.

A good explanation of the differences between bind and bind-dlz is at http://bind-dlz.sourceforge.net/