I got this working by compiling it in a subdirectory one level up from the CMSSW_7_5_3_patch1/src/ level. (i.e. CMSSW_7_5_3_patch1/src/PixelAnalyzers/runSiPixelAnalyzer.py)
Should work in CMSSW_7_5_3_patch1, using some random 13 tev pp data file for now, which was taken with a 7_4 GT. The GT used here is a 7_5 one, so maybe there will be some discrepancies based on a GT mismatch... will have to see