Read that article I linked to: They "why" is explicit: They know that by targeting bands (in any genre) that are not in the mainstream they can be seen as hip to the mainstream. They are not looking to snagging fans of those bands but people who desperately seek to be cool by chasing what is hip - which is a much much bigger market. That is the hip by association that trickknee refers to.
If you ask "why those bands", again see the article. Scion has people who look for bands that are not in the mainstream and toss them aside once the bands start to get popular. What was new to me was that Scion was doing 250 pressings of underground hip hop vinyl as far back as 2004. That they were pressing vinyl shouldnt be surprising. I mean if they figured out that underground bands were what they needed to market themselves as a hip car, vinyl would be the next step. From there they look to other underground scenes that are vinyl obsessed.
A few years ago, there was a huff in San Francisco because an ad agency hired some taggers to bomb parts of the city with a product name and slogan. It took a few days (and one of the taggers getting popped) for the city to figure out that it was an ad campaign. The agency tried to explain itself by saying that this was the "cutting edge" of "guerrilla marketing." They still got fined something like $20,000 (which I assume they settled for half that, less than what they got paid for the campaign), but the spokesperson for the agency considered it a success. By using tagging and, ironically, by getting busted they were able to brand the product as rebellious, something that always sells. Plus they got way more news coverage than they would have had not they been busted. Each story mentioned the product, thus getting the name out there and reenforcing the rebelliousness of the product's user. I am pretty sure that the product was something like an energy drink - whatever it was, it wasnt anything that would appeal to people who would take offense of the tagging.
While Scion doesnt have people out there spraypainting their name about (though they do have millions of stickers made and given away for free, and stuck up on lamp posts and like places), the principle is still the same...and it is part of mainstream marketing culture.
In other news
http://www.sfgate.com/news/article/Beastie-Boys-rapper-s-will-bars-ad-use-of-his-work-3778509.php