Can users sign up for membership on one site and it give them access to that and another site on dif

When a user signs up for membership on on site ( http://www.siteA.com multi-site) can I give then access to another site (www.siteB.com)
What I am trying to do is use another domain with different hosting to make a site with videos (training lectures). I dont want to consume the site (www.siteA.com multisite -hostgator) with all the training material- videos I made for uses to learn the multi-site . I want to use another hosting account with different host. But I dont want the user to go through the membership process twice, plus if I delete them from my mulit-site then I will not have to do it again on the other site.