I hadn't thought about the combo of them possibly helping the one with higher trust bring up the trust of a lower trust site, but that could also work in the opposite way. I would hate to combine them into one Google webmaster tools account to risk it based on the roll of the dice.
As to blackhat versus whitehat, I'm not trying to scam Google or the others. I have multiple sites with well established followings/communities that likely all have good trust level, as they rank fairly well for their respective terms.
Matt Cutts from Google has said that Google discounts links known to be advertising (i.e. paid text links). That makes me feel as though since google is looking for unbiased "votes" for your site that they may also discount the value for a link if they know you control site A that links to site B.