A Yellow Gatso that is facing away from you as you approach it (i.e. on your side of the road it would take a shot of the rear of your number plate) CANNOT legally take a photo of you travelling towards it at illegal speeds.
Firstly, it cannot accurately determine your speed when you approach it (as opposed to travelling away from it).
Secondly, the lines that are on the other side of the road are for the purpose of people trying to 'avoid' the gatso, or overtaking, and .....
Thirdly, if one of those things flashed me in the face whilst driving towards it (bearing in mind how bright they flash), and I crashed, I would have a VERY strong case in court that the flash caused me to crash!
So, in short, No, it cant cover both sides of the road for two alternate lanes of traffic. It can cover the otherside of the road for cars overtaking or avoiding the Gatso.