Is there any significance in the alliteration between Candy, Crooks, Curley's Wife, Curley, and Carlson?

The alliteration is likely meant to subtly signal that George and Lennie are outsiders on the ranch, as they are the only ones without similar C-starting names. As the other answer mentions, the "C" is a hard sound, reflecting the harshness of the people who have been working on the ranch.
There are other reasons for the alliteration too. In a way, Curley's wife, Crooks, Candy, Curley, and Carson are all lonely people, alienated in their own ways. Curley's wife gets lonesome and is viewed with disdain by all the men on the ranch. Her husband treats her like an object. Curley is angry and insecure. Crooks is alienated because he is a black man in a prejudiced society. Candy is all alone save for his dog, which gets shot by Carlson, who hates the dog's smell. Like George and Lennie, all of these people dream of a better, more fulfilling life. And for all of them, as for George and Lennie, these dreams prove elusive.

The alliteration of Curly, Candy, Carson, and others serves a couple of important functions. Their names beginning with “C,” a harsh consonant sound, communicates a sense of the harshness of the lives they lead and the ways it hardened them. It also sets Lennie and George apart as outsiders, solidifying that they can never fully join the others. They haven’t accepted this life as the extent of what is possible, and want to escape it for something more; the alliteration of the other characters subtly reinforces this divide. And while Slim’s name doesn’t start with C, this does set him apart as the leader of the rest of the ranch workers. Names are important in a story. Common writing advice is to never alliterate character names, so any time names are this similar it’s likely for a reason.