On HubPages (or a lot of other writing/content sites) a person doesn't need to be a gifted writer in order to earn. What matters when it comes to earning is that the person writes about what a lot of people search for. Generally, a person just needs to have a basic ability to put together a grammatically correct and spelling-error-free piece of writing. Grammar-check and spell-check programs can eliminate the glaring errors, and if a few errors get by it won't be too harmful in terms of earning.
In other words, a person doesn't need to have great style and ability to earn - only the basic ability to put together several paragraphs.
A Hubber can put together a really amazing piece of creative writing, but even the most amazing piece of creative writing won't necessarily earn.
Then again, however, having good style can attract Hub followers or other readers, which can factor into the writer's overall HubScore and get a Hubber more visibility. Also, with Hubs that are voted "up", rather than "down", the individual Hub's score contribute to the writer's overall score. The writer who can put together a Hub that has substance and/or useful information with style is more likely to put together a Hub that would be considered "unique" (as opposed to "all the other articles on the Web about the same subject).
So, style helps but isn't the most important thing, by any means. Writing that doesn't "horrify" readers with its bad grammar and lack of substance is pretty much all anyone needs to earn, provided they write on subjects that keep showing up in the search engines.