I assumed that this was official art due to the link of the site on the bottom of the picture.
Also, I'm uncertain about a couple of things. 1) That thing at the top shooting lasers looks a lot like the boss of the extra scenario of the first OG game. I don't remember what it was called, though. Can someone verify that? 2) I have no idea what that mech right of the thing mentioned previously is. Too small for me to see. It has wings, but I still can't tell what it is.
If I had to take a guess that mech has to be the Angelg, you can sorta make out the body design just a bit and the wings look similar. Still dont know why OG2 mechs are put into an OG1 scenario but still a good picture