This is something I’ve encountered a lot with SRS (outside of WaniKani) as well. For WaniKani specifically, here’s how I view it:
If you encounter two cards in a row, and they share the same kanji and pronunciation that you did not remember (but let’s assume you recalled everything else correctly), you only need one of the cards to reset to Guru to having the kanji and pronunciation come up in reviews more often. The goal is to learn the kanji and pronunciation, and you can do that with one card.
If you force the second card to be wrong, then you’ll end up with two similar cards going to Guru. This means you’ll be viewing the kanji/pronunciation more often, and that can potentially interfere with the spacing of the SRS.
Thus, I would say if you recognize the kanji/pronunciation on the second card due to having looked it up on the first, you absolutely want the second card marked as correct to prevent it from interfering with re-learning from Guru.
But what if you need to review both vocabulary to learn them better? Maybe it’s better to get both wrong and sent back to Guru (edit: and that will still happen if you get the meaning wrong), but you’ll be learning so much vocabulary through WaniKani, and if you’re using an alternate source for learning vocabulary you’ll be learning so much there, and when reading native material you’ll encounter so much there, that I don’t think it will hurt much in the long run to mark the second as correct for having “cheated” from reviewing the first.
This is what I feel is right and works for me. Others will disagree, and will find resetting both to Guru works better for them.