Considering how similar licenses work, I'd guess that "resale" means bundling it in a project you hand off to a client whereas "unlimited websites" means using it in a project you keep the ownership of.
Not sure how this works for SaaS projects, though.
"Unlimited websites" includes websites for clients' projects (commercial). "Resale in product" means distributing the plugin in an application/product (ex. CMS) for sale (this includes usage in SaaS project).
Other question: How can you use a JS library without having the source? ... I mean, how do you make sure that it remains closed source? As far as I know obfuscating and minifying is very easy to overcome. Do you have any special techniques?
Not sure how this works for SaaS projects, though.