Akatsukami is correct. If the SYSUT2 DD statement specifies an internal reader, IEBGENER will operate it as a sequential data set. It is probably a good idea to specify RECFM=F,LRECL=80,BLKSIZE=80. I recall one incident where it behaved strangely when those DCB parameters were not specified discussed on this board.
A properly written program can interact with JESx to obtain the job ID of the submitted job if it detects the data set is an internal reader.
To be honest, I do not know how to detect that the data set is assigned to an internal reader without doing more research than I'm willing to invest in the project at this time.