Allow me to answer your question with a question.
Is it your plan to go from 1 to 60 on WaniKani without ever engaging with the language in the wild? WK has some weird kanji and uncommon words for sure, but the majority of them are useful and you stand a good chance of seeing them in any book you open or any street sign you walk past in Japan.
If you want to zealously guard against “poisoning” your SRS, you would be forced to study in isolation for the entire year (at minimum) that it takes to finish the course, let alone burn everything. I can tell you from personal experience that without real-world exposure to Japanese, all the reviewing in the world won’t do you any good. You need to have something practical for these words to latch onto, so they can make connections and become real practical knowledge rather than just data points you’ve memorized.
My go-to example is 鎮魂, which you’ll learn at level 55. It uses two complicated kanji and has no cultural equivalent in English. I was fully expecting it to be a terrible leech, but as luck would have it, shortly after learning that word on WK I saw it in a manga I was reading and, as a result, I have never once forgotten it. Far from being detrimental, it was actually incredibly helpful for me to see that word in the wild, in a context where I understood the significance behind it and could get a feel for how it might actually be used.
As far as I’m concerned, SRS is best for helping you get a lot of words into your medium-long-term memory so you can reinforce them in real material. There are quite a few words from low WK levels that I’ve completely forgotten despite burning them ages ago, but the ones that have stuck with me are those that I’ve seen elsewhere and have found practical use for. Just remember that SRS is a tool, not the end goal.
(I do think that if you go in and scroll through all your upcoming items in order to “refresh” on them right before studying, that’s no good. At that point you’re just cramming into short-term memory and that probably doesn’t help.)