The auras have always worked fro me.

Are you sure that your units were not affected?  The auras modify the base values, so you may have missed it.  Hover your mouse over the defense of your units, and see whether there is a base value.  If there's one, it's due to the Aura enchantment.

See the example - these units were trained in an essence 3 fortress.

Also, if the enchantment modifies health, it's adding to the base value of six health for normal trained units, and the health of the trained unit will be an integer multiple of the base value plus twice the unit's level (for Wraiths [Resoln] and Amarians [New Pariden], the health bonus from levels is only one health per level, while for Ironeers [Gilden] the health bonus is three health per level).

So for a three person unit:

           Unit_health = 3 *(base_health + unit_level*health_per_level)

For a seven person unit:

           Unit_health = 7 *(base_health + unit_level*health_per_level)

base_health = 6 + bonuses from enchantments, structures, etc.