I haven't personally done it, but from what I've heard, porting things to z/OS UNIX can be rather painful, due to its use of EBCDIC, and being based on an older UNIX standard (UNIX 95) which means it is missing many newer APIs (for example openat and friends).
IBM has now added to z/OS the ability to run z/Linux Docker containers (a feature they call "zCX"), which run in a hypervisor built in to the OS. It is a lot easier to just run the software under Linux, which is all ASCII/UTF-8 and has pretty up-to-date APIs (even though few Linux distributions have formal UNIX certification, Linux generally implements all the standard UNIX APIs, except for obscure things with dubious value and little use). When it is just VMs on the same machine, network communication between two operating systems can be very fast.
I don't think EBCDIC use is mandatory. It was a while ago, but I did some ports for that Unix, and I don't remember EBCDIC being an issue. Of course, z/Linux is even easier.
IBM has now added to z/OS the ability to run z/Linux Docker containers (a feature they call "zCX"), which run in a hypervisor built in to the OS. It is a lot easier to just run the software under Linux, which is all ASCII/UTF-8 and has pretty up-to-date APIs (even though few Linux distributions have formal UNIX certification, Linux generally implements all the standard UNIX APIs, except for obscure things with dubious value and little use). When it is just VMs on the same machine, network communication between two operating systems can be very fast.