I built my traps up doing tons of upright rows and have not experienced any adverse affects to my rotator cuff, but people respond to exercises differently.I have heard upright rows have the potential to damage the rotator cup from several different sources though.
I think the most productive exercises I have ever used for trap development are repetition snatches and cleans from the hang position, and single-arm snatches with either a kettlebell or dumbell.Lacking the technique to do snatches or cleans, I think high-rep dumbell shrugs with an isometric contraction at the top of each rep would be a good trap builder.But this is from the fact that my traps always responded to lots of volume as opposed to lots of weight.