Yeah. It’s bad for them.
It goes beyond a question of if the environment is bad for it. It is, and can be ….to degrees from “not-ideal” to life-threatening, animal-cruelty-charges bad. That matters. Be realistic about how sanitary the home is. Garbage and rotting food and dilapidated structures can seriously harm or kill a pet.
But what’s really bad for an animal is an owner who does not or can’t prioritize giving the pet proper care. That goes for any pet owner with or without hoarding, but it’s much harder to manage with hoarding.
If you are sure you only want one pet - and that one pet is spayed/neutered (last thing a hoarder house needs is a litter of any kind. The babies often die; the mom scrawns out and gets mange; don’t let it happen), dewormed, vaccinated, flea treated, provided for all necessities including vet care, diet, waste cleanup, exercise, etc. with hair and nails that are trimmed as needed - then it likely won’t be taken away from you even if there is a hoard. Meeting those needs shows care and responsibility.
Otherwise, you’re gonna be on thin ice: if they don’t take it from you, they probably should.
The bottom line is deciding how much an animal means to you and if you can prioritize it enough to do whatever you need to do. Whether that is clear and maintain a safe zone for it, make a habit of walking it / cleaning up its poop when you don’t feel like it, save money for surprise vet care needs, or get your life together so you’re in a better position to care for a dog. You can love an animal all you want, but love is only as good as the lover. Don’t get a dog or any pet if you already know you have no energy or ability to do anything to clean up after yourself. You won’t be able to clean up after a pet either.
If you have a pet, with or without a non-animal hoarding situation in your home, be what your pet deserves. Put it first. Make sure it has everything mentioned above to show you care. If you do that, your pet might be ok and probably won’t get taken from you. If it does, you have a stronger case for why it shouldn’t be.
I personally won’t try to get a well-cared for pet taken away from a person whose house is condemned for hoarding if the animal has access to clean water & food, freedom to move around an area free from hazardous conditions and waste accumulation, a healthy body condition score (usually 4, 5, or 6 on the dog body condition scale, look it up), and necessary vet care as needed by a licensed and practicing vet.
A vet. Not some trashy person involved with drugs who docks ears for dogfighters and/or claims to be raised with dogs on a farm so they know how to do everything themselves. People who say that are often backyard breeders whose practices harm dogs. Or at best, aren’t reliable. Go to a vet, or at least a reputable low-cost clinic. For help finding low-cost shots, spay/neuter, or vet care, call dog rescues and shelters and ask for help with those things until someone refers you to one that can get you an appointment or tell you when and where to walk-in.
But get your dog what it needs. Keep it safe and healthy, clean and fed and hydrated. Groomed and socialized. Happy and exercised. Show your effort. Hoarder’s house situation or not, if you know you will provide that, your dog will be ok. Just be prepared - it’s a lot of effort.