Prepare the grill for direct cooking over medium heat (350° to 450°F).
Lightly brush the sausages with oil. Whisk 2 tablespoons of the honey, the lime juice, and vinegar, and then brush all over the nectarine halves. Save the remaining honey-lime mixture for basting the nectarines on the grill.
Grill the sausages over direct medium heat, with the lid closed, until fully cooked (160°F), 10 to 15 minutes, turning occasionally. At the same time, grill the nectarine halves over direct medium heat until browned in spots and warm throughout, 8 to 10 minutes, turning occasionally and basting with the remaining honey-lime mixture each time they are turned. Remove from the grill as they are done.
Lightly brush both sides of the baguette slices with oil, and then grill over direct medium heat until toasted, 1 to 2 minutes, turning once.
Mix the remaining ¼ cup honey with the mustard.
Cut the sausages lengthwise, and then crosswise into thirds (to fit the crostini). Cut the nectarines into thin slices. Lightly spread honey mustard on one side of each baguette slice. Top each baguette slice with one nectarine slice and one sausage piece. Serve right away.