Flashback was the first to use heartlining, (other than pipe-line coasters?). Since then ALL Intamin's (and later B&M's when it was formed) use it. I dont think vekoma or arrow ever did. Thats why arrow and vekoma dont't have inline-twists, the G's would be insane without heartlining.
Btw, heartlining was werner stengel's innovation, he designed flashback and "invented" the heartline (genius!)!
Flashback is rough because of it's age, and I heard rumors that Six Flags "butchered" the ride, because the heartlining didn't look right to them, so they made modifications to the track.