Does LeGuin draw any explicit contrasts between Omelas and any other place?

Yes, LeGuin does make explicit contrasts between Omelas and other places.

While she does not explicitly name another place, she does compare the people of Omelas to "us." In this way, she contrasts Omelas with the rest of the world.

She says that they were happy, but not simple. She says that we have a "bad habit" of equating happiness and stupidity. For these people, however, they were both happy and intelligent.

Furthermore, LeGuin explains that unlike other nations, the people of Omelas do not have a monarchy, slavery, a stock exchange, etc. Here, she compares their society to much of our world.