Just like those professionaly sponsored footy and cricket matches they'll paint a slanting commercial logo on the surface of the water to catch the cameras at just the right angle.
Rabelais, you're surprisingly accurate - rather like Chelsea, Arsenal and Man U, the Oxford & Cambridge teams have long moved away from putting their best 8 undergraduate rowers into their boat in favour of importing a team of international stars specifically for the purpose of rowing in the event (though they aren't paid 50 grand a week).