I think you would be ok to embed the trailers as they are for promoting the games themselves, you are not altering them in any way, you are not using them to highlight some other competing product.

I would make sure to track down the official links and credit which ever account originally posted them.

If anyone has other thoughts/opinions/facts, please feel free to chime in.

When I post from a pro account on vimeo, I can control whether or not someone can embed elsewhere. I think if you are posting on youtube, you just don't care/seeking adsense clicks from whatever source.