On Vader’s side he would surely feel something, even for just a brief moment, a remnant of his past life flashing in his mind. If we just stick to the movie, C3PO’s memories was wiped out at the end of ROTS at Senator Organa’s order. But yes it would be interesting to see the interactions between Vader/Anakin and R2D2 & C3PO outside of the original trilogy’s context .