I'm so glad to hear you're adopting a greyhound!
Some greyhounds are wonderful and gentle with small animals, and some are highly predatory.
If the rescue you are going to has their greys in foster homes, they may know exactly how the dog will be with cats, other dogs, and kids too.
Also, like many other dogs, yours may be fine with his/her "own" cats, but want to chase strange cats.
Getting a dog who is in foster care has other advantages as well. The dog will probably be housetrained, know how to go up stairs and walk on bare floors, be used to living in a home environment, etc. Greyhounds straight from the track generally do not know how to do any of these things, since the only surfaces they have ever walked on is bare ground, and the only place they have lived is a cage.
And I would certainly not bring a dog who is predatory towards cats into my home. Accidents happen all the time, and can be fatal for the cat, plus it's very stressful trying to keep animals separated all the time.
There are so many greyhounds needing homes, I'm sure you'll find one that right for you!
Looking forward to seeing pics.