What do you mean who was his "rival"? Marcelo ran in a pretty bad team, or rather bunch of teams as it changed a lot. Results weren't that good and he scored no points in the half a year he was in CART. He was the Toyota Atlantic Champion though.
The trucks aren't particularly dangerous. High speed oval racing however was, especially before the HANS and SAFER barriers which has turned fatal accidents into minor injury accidents.
Back on topic though, Jovy Marcelo crash is considered to be the lightest among indy crashes that claimed a life of a driver, on the other hand, however crash of Gordon Smiley is considered to be the hardest crash ever on indianapolis.