Does a paladin's Aura of Protection grant summons a bonus to save vs. their summoner's control?

Question

I am wondering if a paladin can boost a summoned demon's saves against hostile effects at all – it's not exactly "friendly" in most cases – and, if the demon does get the paladin's +CHA to saves, if it can use that bonus to break free from control.

While this seems straightforward if you take "friendly" to mean the creature's true intent and beliefs, it is less simple when considering a creature that is being controlled. If someone has been charmed into working as an ally, for example, would they benefit from the paladin's aura?

Aura of Protection

Starting at 6th level, whenever you or a friendly creature within 10 feet of you must make a saving throw, the creature gains a bonus to the saving throw equal to your Charisma modifier (with a minimum bonus of +1). You must be conscious to grant this bonus. At 18th level, the range of this aura increases to 30 feet.

Summon Greater Demon

[...]At the end of each of the demon’s turns, it makes a Charisma saving throw. The demon has disadvantage on this saving throw if you say its true name. On a failed save, the demon continues to obey you. On a successful save, your control of the demon ends for the rest of the duration, and the demon spends its turns pursuing and attacking the nearest non-demons to the best of its ability.[...]

Demons (MM 53)

A mortal who learns a demon's true name can use powerful summoning magic to call the demon from the Abyss and exercise some measure of control over it. However, most demons brought to the Material Plane in this manner do everything in their power to wreak havoc or sow discord and strife.

Answer 1

The demon does not generally benefit from the Paladin's Aura...

We can reference this question on the definition of "hostile", which cites the DMG p.244:

• A friendly creature wants to help the adventurers and wishes for them to succeed.
• An indifferent creature might help or hinder the party, depending on what the creature sees as most beneficial.
• A hostile creature opposes the adventurers and their goals but doesn't necessarily attack them on sight.

Making no assumptions based on D&D lore, which is not inherent to the spell, the wording of Summon Greater Demons actually makes no provisions as to whether the summoned demon is friendly or hostile- compare to Summon Lesser Demons (XGE p.167), which states

The demons are hostile to all creatures

or other conjuration spells, such as Conjure Animals, Conjure Elemental, Conjure Celestial, Conjure Fey, Conjure Minor Elementals, Conjure Woodland Beings (PHB p.225-226), which all explicitly state that the summoned creature(s) is/are

friendly to you and your companions for the duration.

Because a spell does what it says, and nothing more, it cannot be assumed that the demon summoned by Summon Greater Demon is friendly, and therefore does not automatically benefit from the Paladin's Aura.

... unless the demon is somehow already friendly to the Paladin...

The spell makes no provisions that the demon is necessarily hostile, either. It may be possible to summon a friendly demon, but that demon will not automatically be friendly as a consequence of the spell.

For example, if Paladin McLawfulGood had inexplicably made friends with Shadowy the Shadow Demon, and Shadowy had coincidentally (or by DM fiat) been the specific demon summoned by the spell, then according to the above DMG guidelines, Shadowy would benefit from the Paladin's aura.

Note that the spell gives the caster no ability to choose the individual demon that is summoned, but does allow for the possibility that the summoned demon is known, as it includes a small advantage

if you say its true name.

... but possibly only until the demon breaks free

By a strictly RAW reading of the spell, when the demon breaks free, it

spends its turns pursuing and attacking the nearest non-demons to the best of its ability.

This is not an optional clause; therefore, a friendly demon who manages to break control would then be compelled to attack the nearest non-demons. If that happens to include the Paladin or his allies, this is likely to shift the demon directly into the hostile category, and therefore not benefit from the Aura.

That said, there is a lot of ambiguity within this spell (such as whether the demon is compelled to attack, or this simply describes the behavior of most demons), so a reasonable interpretation will ultimately depend on the DM in this slightly absurd scenario.