I tried comparing these two programs by looking at the CPU time for reformatting a large file. The ICEGENER step used on the average, 0.12 CPU seconds while the IEBGENER used on the average, 0.15 CPU seconds. This may not be a huge but if you consider a larger file, then the impact may be noticeable. The drawback is that if there are SYSIN statements specified to ICEGENER, it calls IEBGENER instead.
The JCL to execute ICEGENER is similar to IEBGENER:
//GENER EXEC PGM=ICEGENER//SYSUT1 DD DSN=YOUR.DATA.SET.NAME,DISP=SHR//SYSUT2 DD DSN=YOUR.NEWDATA.SET.NAME,DISP=(,CATLG),// DCB=*.SYSUT1//SYSPRINT DD SYSOUT=*//SYSIN DD DUMMY