Marc is known for speaking to his fans, in fact he's spoken with them about the Half-Life lore through this account. You can see his messages to people through this account here: http://forums.steampowered.com/forums/showthread.php?t=2503050
I emailed the message to the account listed in that...
Marc Laidlaw has confirmed through email that he's no longer a member from Valve. I've opened a discussion about it on the Reddit subforum of Half-Life: https://www.reddit.com/r/HalfLife/comments/3zzmi2/sent_an_email_to_marc_laidlaw_about_hl3_he/
Screenshots of the email: http://imgur.com/a/EfHC5