DOE seems pretty open to LinkedIn, although I’ve been noticing lately that LinkedIn’s own practices are reducing its value. (Progressively hiding more of people’s information unless you pay for a premium service level, which is pretty expensive — I can’t imagine myself or most of my colleagues being willing to pay what they charge.)
Interestingly, DOE blocks GovLoop *subdomains* as being “social media”. Well, duh! But the primary domain is not blocked, so anything that can be addressed as a subdirectory is accessible, but not things that can only be addressed as subdomains.