You can never gain mana when recieving a discount.
This means if an enchantment costs 0 to reveal, and you have a ring which would make you pay 1 less - then you would still pay 0 (and not -1 / recieve 1 mana.)
And yes: a spell can with reduction(s) cost 0 to cast.
The discount rings are quite different though they appear the same at first look.
Some grant discount to a school of spells (holy, nature, arcane etc) , Some grant to a type (Incantation, enchantment, creature) some grant to subtype (Animal, Force, command).
Some of them have additional restrictions such as:
Enchanters ring only on friendly creatures.
Ring of Asyra: must be both holy school and Incantation or Enchantment.
Besides the common "once per round" and "enchantments recieve this when revealling".
I suggest studying whatever ring you include to be sure you got it right.
(i atleast made the mistake of taking wrong discount or forgetting a discount several times for multiple rings or even the same ring over and over.)
To the OP question:
Battle Orders is a Quick Command Spell.
(see Warlord Stats Card)
Ring Of Command says: One Less mana when casting a command spell.
Answer:
Battle orders will recieve 1 mana discount.
PS. If a spell costs 0 mana you must still spend an action or quickcast marker to cast it.
