Given that bestiality is the act of having sex with animals and having sex with animals might be a kink for some, this sounds like a thing that surely happens, but I feel we have to distinguish between zoophilia, bestiality and a fetish first.
I only take the official definitions of the words, wherein zoophilia is defined as a sexual attraction towards animals and bestiality is the act of having sex with animals and not the definitions some zoos invented for themselves. So a zoophile, a person sexually attracted towards animals, can, but doesn't have to be a bestialist. A bestialist, most likely would be a zoophile though. So the question shouldn't really be, if bestiality is a kink (as it only describes a specific act of sex) but if zoophilia (which might have caused said specific act of sex to happen in the first place) is a kink.
So by default a bestialist might be a zoophile, if they feel sexually attracted towards animals. The only instance where a bestialist wouldn't be a zoophile would probably be a person who's more inclined to take an opportunity, rather to act out on attraction, along the lines of: "I'm horny. Oh look, there's a mare over there and she's presenting. Well, a hole is a hole, let's do this!". But then again, if they didn't feel the attraction, it would hardly be a kink. So bestiality in itself is not a kink, but might be a part of a kink.
So the question is, is sexual attraction towards animals, which is what zoophilia is, a kink in and on itself? I guess this very question is, why many zoos try so hard to change the definition of a zoophile, because it might be easy to construe that a specific sexual attraction is a kink. The term zoophilia stems from a list of paraphilias, which invites some less zoo-inclined people to draw this conclusion, which in turn causes some zoos to redefine zoophilia by either changing the definition of the word, or by transporting the original definition to new, different words like "zoosexuality", while also trying to cement it as a proper sexual orientation, like homo-, hetero-, bi- or pansexuality are. And while I see the appeal to want to claim it's a certain thing like a proper sexual orientation, it isn't publicly defined as such. Maybe it happens some day, maybe it won't. But it's certainly not the case as of today.
So zoophilia remains a sexual attraction towards animals, which might mean many things for many people. An orientation for some, a fetish for others. It may indeed be both for different people, given that zoos are just as diverse as anybody else and not many share the exact same views of anybody else.
An additional question would be: Would a kink be that bad? I guess this also depends on who you ask as well, but I give you my opinion here: sexual attraction towards and a sexual act with an animal could be bad, if it only served for human sexual gratification. Sexual gratification is a large motivator that might make some people try to get it no matter the cost. In this case an animal might be abused as a sex toy and not much thought would be wasted on the wellbeing of the animal. That's certainly a form of abuse and should be discouraged. But not every person is driven by this motivator. A common complaint is to train an animal to endure sex against their will. Sadly I have seen this kind of behavior among zoos before and have also been asked a few times if I had any tips on how to train an animal, for example a castrated, male dog who lost his libido with his balls, to have sex with said person, to which my answer always is: "No, I do not know how to train an animal to have sex with you. And if I did, I wouldn't tell, because something like this shouldn't be happening. If your pet is not interested, then simply take that as a 'no' and leave it at that." Sadly, some people can't take a "no" for an answer.
Someone else who fetishizes about having sex with animals and eventually doing so might actually like or even love animals and would think twice about the wellbeing of the animal in question. Someone who is more considerate and compassionate might still tempt an animal to have sex with them, but would be fine with the animal rejecting the offer and wouldn't force it. I've seen examples of such people among zoos as well and I don't mind them at all. I remember someone telling me they had the hots for some local bulls and visiting them regularly, but never doing anything illegal to them and just enjoyed being close to them, maybe fondling them, but only as long as the bulls seemed comfortable with it. If this was the whole truth, then I obviously wouldn't have any problem with that, as long as the place where those encounters happen were public of course. Trespassing is something I can't condone as well, but that's partially unrelated to the ethical treatment of the animal in question. People with those fetishes easily could also own pets or have legal access to the animal in question, so in those cases there's no objection from me.
TL;DR:
To me it's less important if the sexual attraction towards an animal is a fetish or not, than if the person having said fetish is a good person and treats the animal well and can also deal with rejection by said animal. If people treat an animal well, I couldn't care less if it was a fetish or not. If people treat an animal badly, they could even claim to have a legitimate orientation, I'd still condemn them for mistreating an animal.