Sure, but why would you want to?
I/O for stream files/flat files in the IFS is done using APIs, which are much easier to deal with in a language like RPG or COBOL. Use the right tool for the job.
As of V5R4, ILE CL handles streamfile I/O almost the same as ILE RPG, C or COBOL. It’s probably much easier to write in CL, but the APIs will be the same ones. Use the open(), write() and close() APIs. These are listed and described in the Integrated File System APIs topic.
Although these can be easier in ILE CL than other languages, it should probably be done for proofs-of-concept or prototyping or learning, rather than for significant production programming. ILE CL can only include a single procedure in each source module. For some purposes, that is okay for CL.