I brought Bear into my house with 3 cats, and it worked out okay. It definitely depends on both the dog and the cat. Before they placed Bear with me, the trainer made a visit to a home with cats and dogs, to see how Bear would react to cats (with cats that wouldn't be afraid of the dog). He walked up to the cat, sniffed it, wagged his tail, and left it alone. So I felt pretty comfortable bringing him into my house with the cats. Two of my cats did live with a dog for a few months when they were in foster care before I adopted them, and they got along fine there, but that was a few years previous.
I saw Bear twice before I brought him home. Each time, I took a shirt that I had worn and rubbed it all over Bear (especially the groin and the face, where the good smells are!) and then took that shirt home for the cats to smell. I'm not sure if that helped or not, but that's what they trainer suggested.
When I brought Bear home, I kept him on the leash at first to make sure that he wasn't going to do anything to the cats. We hung around a little, just to let the cats get used to the idea that there was a stranger in the house. They had all taken off to the basement, so after 20 minutes or so we took Bear down there and just sat there. He laid down, and eventually the cats started to come out and peak at him (lots of hissing and puffing up from the cats). After we did that for a while, and felt confident that the cats at least had some idea that this big stranger might not be so scary, we went back upstairs and left the cats alone (Bear came upstairs).
Eventually, the cats started sneaking around in the same room as him. Finally, they even started coming up to sniff him. That's as far as it went. No cute interspecies cuddling. But no interspecies warfare either.
I would definitely see if they can arrange a visit with the dog to a home with some dog-friendly cats to see how he reacts. If he takes off chasing all the cats, then you may have a problem. Perhaps, if it's early enough in the training, they could find a different dog for you (or acclimate the dog to cats).
Other than that, my advice is to just take it really slow and let the cats check the dog out on their own terms. Definitely don't pick up the cat and hold it nose to nose with the dog. Just let the cat check out the dog when it's ready.