I love to read (as opposed to everyone else who reads your blog), and want to know what a slush pile reader is. Sounds like an interesting job.
Also, my [friend] is an artist currently illustrating for a column for the [XYZ] newspaper (just so you know someone else would call him an artist too.) and is interested in doing the art on the book covers. Are the book cover designs submitted by the author, or does the publisher supply it? Who would he contact, or how would he get involved in this branch of the business?
Slush Pile Reader -- A slush pile is a stack of unsolicited manuscripts. A slush pile reader is someone who reads through those manuscripts and pulls out any that look interesting. Generally, these readers are employees or assistants. Some companies may hire out the reading. Slush readers are often paid in book copies, rather than with real money. To be considered as a reader, you need to know someone in the company who will recommend you as a judicious and discriminating reader.
Book Covers -- The author gets little to no say in the book cover design. Some publishing companies (big ones) have an in-house designer, but most of them outsource that work. I have two or three artists that I work with on cover designs, but I'm always keeping my eye open for new ones. Designing book covers requires more than the ability to draw well. This is the book's #1 marketing tool, so some knowledge of marketing and industry trends is needed. You also have to be able to create and manipulate everything in a digital format. Any experience as a graphic designer will help.
Put together a portfolio and a resume. Experience counts for a lot. If he's never done book covers before, have him create a few as samples. Then contact the publishing company and ask how to submit your portfolio for consideration. Some companies might want to see hard copies, others will want you to e-mail it to them.