Do you have a link to this application's website? Maybe we could determine why it might be stuck to a limited set of OS releases. If a software can't keep up with a limited subset of OS updates, maybe they are concerned more with costs then security.
The OP is happily incorrect on the 5.0 issue. CentOS 5.x is fully supported under Paralells Pro X for Linux from 10.1.0 and up (current release is 10.3.1). I know this because I run it on CentOS 5.2
HTH, -Ray