Hoever moves to Bramall Lane on-loan to the end of the season.
Speaking about his arrival, Blades manager Chris Wilder said: "It is no secret that we need to strengthen on the right side, and during discussions about personnel in that area going forward, Ki's name was always one which featured prominently as he possesses quality. The loan market tends to be one which intensifies later in the window, so to have this deal completed is a huge boost for us.
"Ki is still a young man, but he's experienced plenty in his early career. To have been at some of the clubs he has represented just shows how highly rated he is. What I like about him though is the desire to go and play.
"He now knows what it takes to be successful at this level, and by his own admission, he's really matured, on and off the pitch. He's ready to take the next opportunity in his career and we're delighted to have added him to our squad, not least for balance."