I have quite a bit of nitrates in my tank and never had a problem with SPS. Now my nitrates are around 5ppm but last month it was at 40ppm.
My sps always have been doing great no matter what the nitrates. Recently I bought 10 fresh cut SPS frags that were kept in ULN tank and very light in color, almost bleached. I only lost one frag and they other are starting to color up nicely, not turning brown at all, rather getting some nice fluoresence and colors.