I'm living with two dogs who both have high prey drives: Kaya, an Aussie Cattle Dog mix, and Izzy, a border collie. I'd had Kaya for a few years before bringing a rabbit into the household, and wasn't sure how she'd react. Well, the first time Kaya saw Rufus she literally stood outside of his cage trembling and drooling, she wanted to get to him that badly. (She once killed a young groundhog when we were out on a walk in the woods.) It took me quite some time working with her, but finally got her to a point where I could leave the rabbits with her and not worry that she'd attack. (In fact, at one point a few years ago she sort of rescued the bunnies when a feral cat attempted to enter the yard and attack the rabbits...Kaya went ballistic, barking at the cat and then running into the house to fetch me, as I'd gone inside to pour myself a drink.) Today I trust Kaya almost implicitly with the rabbits; however, I still won't leave her completely alone with them in the house because she can get snappy if there is food around. Outdoors, she won't go near them if they're running about...if one of the rabbits approaches her when she's lying down outside, she gets up and walks away.)
Izzy is now 7 months old, and he too has a high prey drive. I won't leave him alone with the bunnies, but I do make sure he has supervised exposure to them every day, just as I did with Kaya. Izzy will now walk into the rabbit room and look at the bunnies, or they will come out and hop around him, and he doesn't touch them. Doesn't mean he wouldn't, given the chance; a dog with high prey drive (imo) can never be completely trusted with a small animal. If the animal suddenly takes off in a hurry, that alone can trigger the dog to chase, and chase can trigger capture, and worse. For instance, there was an incident at my home several years ago, where my sister and other family members were visiting for dinner. My sister had brought her dog Lassie. Lassie too has a somewhat high prey drive, and while she will tolerate a cat, she is always *on the alert*, never having really been trained to not go after them. Now, Lassie had met Fritz, the cat I used to have, numerous times; Fritz even used to go up to Lassie and sometimes rub against her...but he sensed her nervousness, and he would be cautious around her. On that day my cat Fritz was sitting on the back of the sofa, and something (not sure what, I wasn't in the room) must have startled him because he leapt off the back of the sofa. Upon seeing this sudden movement Lassie jumped up and ran at Fritz, Fritz reacted by hissing, which triggered Lassie even more, and she attacked him. All of the commotion triggered my dog, Kaya, and she ran over and joined in. The two dogs had Fritz pinned against the door and both were attacking him...I ran into the room immediately and did the first thing I could think of; I opened the door so Fritz could escape. In the end Fritz wasn't hurt, just very shaken up, but had I not been there to intervene he might have been seriously injured or even killed. And as I said, one of the dogs was Kaya, who slept regularly with Fritz and would nuzzle him. Prey drive in a dog, if it's high, can be very dangerous, and always has to be kept in mind when keeping more than one species in the home.
My belief tends to be that, even if you can't get a dog to be completely trustworthy around other pets - though many are - then at least keep reinforcing the fact that it's wrong to do harm to them, and make sure they are consistently exposed to them -- in safe conditions. I do believe that this once saved Yofi's life; through a mistake of my own, one day I left the house to go shopping, but hadn't realized that the door to the rabbit room wasn't shut tight enough to latch. When I came home about an hour later there was Kaya sitting in the living room with Yofi running all around her. And back in those days he was a pest extraordinaire with Kaya, constantly trying to follow her whenever I'd let him out. So (thankfully!!) Kaya learned what she'd been taught, and didn't touch Yofi...who I'm sure must have been driving her crazy the entire time I was gone. Things could have been much different and I'm thankful every day that nothing bad happened to Yofi because of my oversight, but I really do believe that teaching a dog to respect the other pets in the family is of utmost importance. Even if there will never be a planned interaction with them, one never knows when something unexpected happens, so teaching them this is imperative.