The RAT can drive a hyd pump, or an electrical generator or both. The VC10 even had two RATs, one elec and one hyd.
The problem is that the same word RAT is used for all types so if you have met an el-RAT in your past life, you might think that the hyd-RAT on your present aircraft can produce electricity.
On the B757 the issue is further clouded by the little hydraulically driven electrical generator fitted to some aircraft.