Actually, something like this just happened a few weeks ago at Bay Meadows. The answer is that it would depend on the state laws that apply to Fairgrounds -- At Bay Meadows, a race finished 5-2-4. There was an inquiry, the #2 against the #5 and the #4 against the #2. The stewards ruled the #5 was dq\'d from first to second for interference with the #2. Then, the stewards ruled the #2 was dq\'d from first and placed third for interfering the #4. The final result was 5-4-2.
The reason, according to state law is that the stewards are to take each indicent in the order it happened, in the case at bay meadows, the 5 did interfer with the 2, then the 2 interefered with the 4. So the 5, while being dq\'d, still ended up the official winner.