Many people are very concerned that the person doing the writing for them won't have their voice and hence the blog will sound as if someone else has written it.
Let me assure that it isn’t really a big problem.
Most professional content developers are extremely conscious of trying to write the content in the client’s voice, putting aside their own style and personality, and if they're good they're able to do that quite well.
As an extra precaution many content developers, myself included, will interview the person for whom they are writing, to ensure that we pick up on the nuances that should be heard in the article.
Most content developers will also spend quite a bit of time speaking with our clients before we start to write and so we learn their voice and communications style. Only then do we start to write.
So put your worries aside. Hire your content developer after careful review and remember you have the ability to approve your article or not. If you don't think that they've nailed it ask for a revision. Most content developers want to make the client happy and will revise accordingly.