I don't know if it is a lost cause but I suspect it depends on the dog. Some dogs get the taste of sharp claws on the nose and learn to respect, others it just makes em dislike cats more. If the dog is calm, the cats have a place to escape, it might be worth the effort. I know the Baqel howls at cats, they run, he thimks they are prey. I have a feral cat I've taken to protecting in my back yard. He does run, kinda ignores the Bagel and the Bagel learned to except him as sharing his backyard. I was surprised, but as long as the cat is contented and the Bagel isn't hurt, I am delighted. Took about two months before the Bagel lost interest. Now the cat has numerous safe places and is not in any danger and is not an indoor cat! I hope it helps but I'm no expert, I'm now allergic to cat dander so no cats in the house for me or the Bagel.
I kind of think it depends on what they mean by not cat friendly. Does he chase them like Maggie does because its really fun and then stop when they stop and not know what to do next or is he angry, aggressive, growling and wanting to hurt the cat? I have four cats. Two have taught Maggie that they will claw her face if she gets too close, one has finally learned to stop running. She not only stops she rubs on Maggie's face. The fourth still runs and Maggie still chases unless I get there first. However, she does not try to hurt any of them including the one that runs.
I agree with jassy, there is a difference between not being cat friendly and being a kitty killer. We had the shelter cat test Violet and she passed fine. Once we got her home, she ignored Phoebe for the first few weeks. Then she decided kitty was interesting and started barking at and chasing Phoebe. Phoebe growls and hisses at her and pops her with her paw and Violet just barks. So had she done that at the shelter, they may have labeled her as not being cat friendly, but she really just wants to play. As time has passed, they are becoming friendly with each other and Vi rarely barks at or chases her and Phoebe doesn't growl and hiss.
Now there is a lab mix next door that goes beyond and is a cat killer. Matter of fact, she killed my last cat and it took me 3 years to finally get another cat, my Phoebe. No cat is safe around that dog as she tore through a screen to get at my Jasper.
I'd ask the shelter what type of behavior she exhibits around cats. If it's just chasing and barking, I wouldn't be too concerned, but if it's aggressive and threatening, I would have to pass on the pup. Let us know what happens.