How does the Oathbow's benefit to ranged attacks interact with the Arcane Archer fighter's Arcane Shot options Piercing/Seeking Arrow?

Question

Part of the description of the oathbow magic item says:

When you make a ranged attack roll with this weapon against your sworn enemy, you have advantage on the roll. In addition, your target gains no benefit from cover, other than total cover, and you suffer no disadvantage due to long range. If the attack hits, your sworn enemy takes an extra 3d6 piercing damage.

However, the Arcane Archer fighter archetype from Xanathar's Guide to Everything (previously appearing in UA: Revised Subclasses) has the ability to imbue their arrows with magic. Two of the Arcane Shot options seem like they might conflict with the oathbow's trigger condition.

The description of Piercing Arrow says, in part (XGtE, p. 29; identical to the version from UA:RS):

[...] When you use this option, you don’t make an attack roll for the attack. Instead, the arrow shoots forward in a line, which is 1 foot wide and 30 feet long, before disappearing. [...] Each creature in that line must make a Dexterity saving throw. On a failed save, a creature takes damage as if it were hit by the arrow, plus an extra 1d6 piercing damage. On a successful save, a target takes half as much damage.

The description of Seeking Arrow similarly says (XGtE, p. 30; also identical to the UA:RS version):

[...] When you use this option, you don’t make an attack roll for the attack. Instead, choose one creature you have seen in the past minute. The arrow flies toward that creature, moving around corners if necessary and ignoring three-quarters cover and half cover. If the target is within the weapon’s range and there is a path large enough for the arrow to travel to the target, the target must make a Dexterity saving throw. [...] On a failed save, the target takes damage as if it were hit by the arrow, plus an extra 1d6 force damage, and you learn the target’s current location. On a successful save, the target takes half as much damage, and you don’t learn its location.

So how does the oathbow interact with these 2 Arcane Shot options by RAW?

I know some situations override things going both ways in favor of exploitation and prevention.

Does the class skill let you bypass the attack roll while getting the oathbow's power buff? Or do you not get the buff?

Answer 1

You don't get the buff, because the very first part of Oathbow reads:

When you make a ranged Attack roll

And with these spells, you don't make a ranged Attack roll. So nothing happens with the Oathbow.

Answer 2

Piercing arrow and seeking arrow require saving throws from the target. There is no attack roll, ranged or otherwise. Oathbow effects would not apply with these attacks, just as Oathbow effects would not apply with a Fireball or a Lightning Bolt. Applying damage “as if it were hit with the arrow” emulates the magical effect. Lightning Bolt could say “as if it were hit by lightning from the sky,” but it would not have been not hit by lightning from the sky; rather it would have been hit by a spell.

Answer 3

This is unclear. The main issue is this line:

On a failed save, a target takes damage as if it were hit by the arrow, plus an extra 1d6 piercing damage.

"As if it where hit with the arrow". This is talking about a counter-factual; "the arrow didn't hit the target, but we are talking about a situation where it did, and extract from that situation the damage it would do".

What, exactly, is that counter-factual situation emulating?

As if "someone picked up the arrow and hit you on the head"?

As if "someone, not you, shot the arrow and hit the target"?

As if "you instead of using this power made a normal ranged attack on the target, and hit the target"?

I would argue that choice 3 is what people are implicitly emulating. They are applying your dex bonus to damage, any enhancement bonuses, any feats you have, etc.

By RAW, however, the first (someone bonked them on the head with the arrow) is just as supported, in which case the damage should be that of an improvised weapon at most with no modifier to damage from attributes.

When you make a ranged Attack roll with this weapon against your sworn enemy, you have advantage on the roll. In addition, your target gains no benefit from cover, other than total cover, and you suffer no disadvantage due to long range. If the Attack hits, your sworn enemy takes an extra 3d6 piercing damage.

The next question is, does the counter-factual "as if" case involve you making an attack roll before the arrow hits? If that counter-factual "as if" case involves you hitting the target after making a normal attack on them, then "as if the arrow hits" would deal an extra 3d6 piercing damage.

If it doesn't include you making an attack roll before the arrow hits, I'm uncertain where in the rules you can hit a foe with an arrow without first making an attack roll. So the rules are unclear how much damage it does, ignoring this feature entirely.

Or you could choose to read the ranged attack portion as being severable where the hitting is divorced from the attack roll portion, in which case this doesn't apply.