There's nothing wrong with having a group blog. There's also nothing wrong about having guest bloggers. However, the most important thing about blogging is to be personal. This is why so many SEO experts say that it's imperative that you or your direct partners be the primary writers for your blog. But in fact, the one major reason that actually keeps many bloggers from writing on a regular basis is not being sure what to write or how to write it for their intended audience. Enter the ghostwriters.
As you know, ghostwriters are nothing new. It's a pretty old profession. They're also nothing new for SEO. In fact, getting someone to get your ideas and messages across that is a great writer and also good at creating content relevant to both your audience and the search engine algorithms is fantastic. It's just very important that you find someone that can both write and can make you look good at the same time. The last thing you want to happen is someone who's really only blogging for you for the sake of getting exposure for themselves. While it's okay to have a guest post or two every once in a while, it's good to keep the blog subjects in house as much as possible, even if you have to go outside to get it written.
So where can you draw the line between being completely authentic and putting everything into your own words versus hiring someone outside to write for you? There are plenty of people out there happy to write two or three articles a week for you, for a price. While many of these people are often perfectly good writers and have good reputations, you need to keep in mind that you don't want to put the future of your blog or business necessarily in the hands of content creators. Therefore, the best way to go about it is perhaps to have ghostwriters that take your raw ideas and polish them up into something SEO-friendly, readable, and relevant to your current and potential readers and/or clients.
Hiring somebody to write an article for you as a blog contributor when you're really stuck is fine. Just don't rely on them too much. You want you and your blog to become an expert resource. Yes, having other topical experts writing for you is great, but you don't want to depend on them, because they're the ones offering the information and not you, even if it is on your blog. Yes, outside bloggers known in your industry can provide some credibility, but you need to put your names on it. It needs to be someone within the blog ownership itself that blogs the most, even if that person, or those people if you decide to make it a group effort, has someone ghostwriting for them.
So it's not a bad idea to have a ghostwriter working for you, though preferably you want it to be someone consistent. Just make sure that your own voice is heard and that your content is useful and findable. There are ghostwriters that are excellent at this. But still, nothing is better than just putting your own thoughts out there and letting someone tweak it for you. That's the best advice I can give.