The short answer is yes. But I bet some authors are shaking their heads at my assessment. Stop it. It's helpful to outsource blog posts as an author.
If you are engaging in marketing as an author, you will need content. This content is necessary for social media, your website, blog, and elsewhere to introduce you to new readership and engage your fan base. And the odds are good you probably should not be the one writing it.
You aren't objective.
You are too close to you and your writing. Too many writers write to who they think their audiences is--not who they really are. Even if you try to put yourself in your audience's shoes when it comes to marketing messaging, you will most likely miss the mark.
You don't have time.
Aren't you supposed to be writing books to make money? Spending time on blogging or other marketing activities takes away from that. If you even get there. Most authors think they will rock their own content, and then they run out of time. Blogging and other activities to attract a wider audience (and greater income) go out the window.
You aren't that kind of writer.
An inspirational author would probably struggle heavily to write a chemistry text book or a piece of a historical fiction. A science fiction author may not be too good at writing business manuals. Writing for different genres, subjects, and purposes all require different skills, knowledge, and training. The transition to marketing copy is probably harder than you think.
Not only authors but also other busy and successful folks like life coaches, consultants, and startup entrepreneurs happily bank on ghost blogger. Ghost blogging is going to happen and it always has.