依照原文来看，不是。
https://www.aonprd.com/Rules.aspx?Name=Legendary%20Item%20Abilities&Category=Legendary%20Items (https://www.aonprd.com/Rules.aspx?Name=Legendary%20Item%20Abilities&Category=Legendary%20Items)
Foe-Biting: When this item deals damage, its user can use mythic power to double the total amount of damage it deals. If the attack is a normal attack, the bearer can expend one use of legendary power to double the total amount of damage. If the attack is a confirmed critical hit, the bearer must instead expend two uses of legendary power to double the total damage. Damage from weapon special abilities (such as flaming) and precision-based damage are also doubled.
This ability can be applied only to weapons. An item must be a minor or major artifact to have this ability.
这里援引CRB规则-战斗规则中的倍数伤害：
倍数伤害（Multiplying Damage）：一些特殊条件可以让你造成的伤害翻倍，比如成功确认的重击。在此情况下，你需要多次伤害检定（加上所有的修正）并将结果汇总以计算伤害
注意：当你同时应用多项倍数伤害时，每一项对初始伤害分别生效并叠加，而非依次生效并叠乘。
例外：武器正常伤害之外的额外伤害骰，永不会因倍数伤害而翻倍。
【速查】倍率（Multiplying）：当你的某次投骰出现超过一种的倍率时，注意倍率之间并非叠乘，而是叠加为单一倍率——每个额外的倍率将会减1后加至总倍率。举例而言，若你需要添加×2倍率两次，合并后的倍率将为×3，而非×4。
Multiplying Damage: Sometimes you multiply damage by some factor, such as on a critical hit. Roll the damage (with all modifiers) multiple times and total the results.
Note: When you multiply damage more than once, each multiplier works off the original, unmultiplied damage. So if you are asked to double the damage twice, the end result is three times the normal damage.
Exception: Extra damage dice over and above a weapon’s normal damage are never multiplied.
噬敌中特意使用了与CRB中不同的“the total amount of damage”，在此之上，还特意指出了会翻倍武器特殊能力与精准伤害所赋予的伤害骰。按照语义理解，多半是为了与基础的重击规则相区分的。
所以，总的来看，噬敌的翻倍是指“将由本武器造成的此次伤害中，武器伤害骰、武器伤害加值、使用者伤害加值、武器特殊能力伤害、使用者的全部精准伤害，一同翻倍”，即使这是一次确认的×4重击，也可翻倍（当然要多耗1次传说之力）。