No. We are not a plugin for WordPress or any other platform. You will not be able to add SubHub's membership functionality to another website. Our platform is a stand-alone website builder.
However, we have clients that use their main website as a brochure or branding site, then give their SubHub site a subdomain of the main site name. For example, if your other site is called mainsite.com, you could create a subdomain called members.mainsite.com for your SubHub site, then provide a link to it from your primary website's navigation.