The short answer is yes, it is possible for gas to pass around an obstruction, even if the dog is blocked.   For more information on obstructions, I recommend reading this article:

https://www.petmd.com/dog/conditions/digestive/c_multi_gastrointestinal_obstruction

As mentioned in the article above, the most common symptom of blockage is either vomiting, especially after eating, as well as weight loss, lethargy, and diarrhea.