Dave,
Will a remote with v 4.2 software work with a TIU with v 5.0 software?
Yes, it should "work". The questions is, "how well and will there be issues?"
There were significant changes made between DCS 4.2 and 4.3, and additional changes between 4.3 and 5.0. I would strongly advise against mixing DCS versions on a layout.