'nohup' runs a process such that if you log out, it will keep on running, but it is not really needed for SASGSUB.
SASGSUB (the SAS Grid Manager Client Utility) by default submits a SAS program to the grid and returns which allows you to log out while the grid will at some point run the job without user intervention. To get the results of the job, you would you log back in and run SASGSUB again with the option to get the results.