These threads about "authentic" or "indigenous" music are starting to say less and less. I don't think this genre of remix weekenders has anything to do with authenticity per se; it really is just music made by dilletentes. A Mad Decent take on dancehall, for example, is going to sound alien and impassioned to fans of dancehall because it is just that - alien and impassionate to the genre of dancehall. On one hand, taking this approach to making music I think can overthrow genres that may have become formulaic and tired and breathe in a fresh air of life, while on the other hand it can come across as amateur, shallow, opportunistic or, at times, condescending*.
Ultimately it really just comes down to how good the music is. When you start talking about authenticity you run the risk of having a conversation that is far more about you and how you want to feel about yourself than it is about actual music.
* I understand that using the word "condescending" might seem like I'm veering into the kind of personal gripes that I am warning against. I don't mean here condescending in the way that the outside artist is rudely presuming to be on the same level as the "indigenous" ones (a condescension that it would be pretty obviously hypocritical to feel a victim of), but the condescension of the outside artist viewing a scene as a demographic which he might be able to make a quick buck off. This is really a moot point though because these artists rarely ever actually end up selling their tunes to the actual enthusiasts of the genre in question, but rather the mums, sisters, brothers and disinteresed peers of those people.