The 19-year-old substitute's 20-yard chip over Robert Green in a one-on-one with the goalkeeper dropped onto the top of the net in the 77th minute.
Prior to that Carlton Cole had the visitors' best effort, curling wide a 20th-minute shot from a narrow angle while Rovers defender Chris Samba fired over from the edge of the penalty area in the first half.
The game began brightly with debutant Pascal Chimbonda's surging run down the left touchline resulting in James Collins being booked for a foul on Morten Gamst Pedersen. David Dunn lofted over the ninth-minute free-kick which Christopher Samba headed back across goal but the stretching Jason Roberts could not divert the ball in.
Samba was then involved at the other end as some neat interplay between Junior Stanislas and Luis Jimenez set up Cole only for his shot to be blocked by the big Rovers defender.
Cole then shot from a narrow angle but curled his right-footed effort wide of the far post without drawing Paul Robinson into a save.
Samba fired over from the edge of the West Ham box after the visitors had failed to clear Roberts' pull-back.
Three minutes into the second half Cole lashed a 20-yard shot over Robinson's crossbar with Collins' shot from Mark Noble's left-wing corner also too high.
Hoilett's first involvement was to shoot into the side-netting from Dunn's reverse pass in the 68th minute before returning the favour only for the midfielder to shoot straight at Green.
Hoilett should have scored in the 77th minute when Dunn picked him out on a swift counter-attack with an incisive pass. But Green raced out to meet the youngster who was just over with an audacious 20-yard chip.