Well, I was going to include a vehicle or two from the 101 MT Vehicle guide in a couple adventures I was writing, but it's like I don't know what I can and can't use. So I commissioned someone to create something for me (which is a story in itself). I can't use of the things mentioned there unless they were mentioned before.
Big deal.
One or two of the illustrations from 101 Vehicle Guide have appeared in other products. (I'm at work right now so I'm doing this from memory.) The Gram grav tank from the inside cover appeared in GURPS as a merc tank (god knows why the change), and the Trepida grav tank was in multiple TNE books. There may have been some others too.