I'm sure it might happen by a vet driven by money and not ethics. But I would like to think vets are vets because they love animals. If they're about to spay/neuter an animal and their trained knowledge tells them the animal is pregnate, I think they would inform the owner so they could make a decision about the pregnancy.<quoted text>
Ask any vet. Spaying frequently involves aborting a pregnancy in progress. They just don't tell the owners.
Not informing an owner their pet is pregnant and going forth with spaying would seem to have legal consequences if the owner found out.