The latest version of the Goddard Satellite Data Simulation Unit (3.5.1) is available in NU-WRF Version 8 "Bjerknes". The corresponding user guide is available here.
NU-WRF Version 7 "Arthur" Patch 6: v7lis7-3.5.1-p6
The sixth stable patch to NU-WRF Version 7 (v7lis7-3.5.1-p6) was released on 11 January 2016. This will probably be the last version of NU-WRF based on WRF 3.5.1.