Craigslist’s terms of use don’t expressly forbid VPN usage. However, they do prevent users from “bypassing or attempting to bypass [Craigslist’s] moderation efforts”. The service also has a damages clause that allows it to charge you $4 per infraction.
Of course, since you don’t need an account to post under most categories (and there’s no way to prove your account details are genuine in any case), it’s unclear how Craigslist would ever manage this.