Preheat the grill to medium-high. Grill the corn, covered, turning every 2 minutes, until browned, about 8 minutes; transfer to a plate.
Grill the pineapple slices until grill marks appear, about 4 minutes per side. Transfer to a cutting board and coarsely chop; place in a medium bowl. Cut the corn kernels from the cob and add to the pineapple.
In a medium bowl, whisk together the olive oil, chipotle, vinegar, lime juice and sugar; season with salt. Brush the salmon steaks with 2 tablespoons chipotle vinaigrette. Grill the salmon, turning once, for 8 minutes for medium-rare.
Stir the cilantro and onion into the grilled corn and pineapple. Stir in the remaining vinaigrette and serve with the salmon.