I let my guinea pigs run around my room a little bit, and normally my dog will walk in the midst of them playing. I would expect it to be a cute little duo, but I am afraid that my dog may be a precaution. His breed is a mix. He is part Schnauzer and part Italian greyhound.
The risk for guinea pigs is always high when mixing with dogs, simply because of their difference in size and guinea pigs' prey instincts that signal to any other animal that they are defenseless.
The exact degree of danger depends on the breed of your dog and how well trained your dog is. According to the American Kennel Club, Italian greyhounds:
are flash-and-dash coursing hounds with an instinct for pursuit.
This is a strong warning signal that your dog, while only part greyhound, will have a natural instinct to chase and even kill your guinea pig rather than befriend it. There are no guarantees, but if you love your pigs, it is best to keep them separate or keep your dog leashed at all times (and under supervision) when in a room together.