I work for a contractor and we developed the site - and we did not have to deal with the security clearances.
We are in the process of migrating it to a SAMHSA.gov. url.SAMHSA does own it, but we are currently managing the site
As for choosing Kentico - I am not on the technical team - but I know that our team did compare several content managment systems and felt that Kentico best met our needs - we are also using the platform for an web-based toolkit for Behavioral Health Recruitment and Retention - so we chose Kentico because it could fufill several of our needs.
Although there is a 'public' part of BHTalk - most of the 'fun' happens in the groups, most of which are 'closed' groups of grantees.