Winger Bennett struck in the fifth minute of added time after Daniel Jones was penalised for bringing down Ashley Barnes.
Andy Williams put Rovers ahead in the 11th minute, firing in at the far post after Charlie Reece had released the overlapping Carl Regan.
Barnes, on loan from Plymouth, levelled six minutes later with his fourth goal in seven games.
The striker scored with a tremendous shot after latching on to a long ball out of defence by Adam El-Abd.
Rovers looked on course for only their third away draw of the season and keeper Mikkel Andersen produced a brilliant save to deny Barnes with his feet.
Both sides finished with 10 men with Brighton substitute Glenn Murray being shown a straight red card following an off-ball incident and Rovers defender Danny Coles followed six minutes later for two bookable offences.