I am involved in a project at the moment, wherein there are rpms installed on the RHEL 6, which do not belong to the original distribution. I have been vested with the task of finding out what are the latest and greatest versions of these rpms, which can go into RHEL 8? When I do a search by rpm name at RPM pbone.net for a specific rpm, say acroread, I also get results which have been tagged against OS versions other than versions of RHEL (for example, in the case of acroread, the search results show OpenSuSE et al., along with RHEL versions). So the question is: excepting the architecture (i.e., i686 or x86_64), would it be correct to assume that the latest and greatest rpm version shown against any of the other various OS versions can be considered for RHEL 8 as well?
Welcome to the forum ! The short answer to your question would be: probably, but not with certainty. Ultimately, the only way you can know the latest version available for RHEL 8 of a given third-party package is by going and checking what the latest version of that package is for RHEL 8. There isn't really any way around that, if you want to be 100% sure.
Now, you could quite possibly script the process of checking that, or at least make it easier to check, if the RPMs in question all come from the same third-party repo or repos, and you can install those repos on both the RHEL 6 and RHEL 8 server.
For example: on the source RHEL 6 system, you could check what version of the package was installed with either a yum list installed <package name> or an rpm -qi <package name> command. On the destination RHEL 8 system, you could then (after installing the version of that third-party repo for RHEL 8) do a yum search <package name> to see what the latest version of that package provided by the repo was.
However, if the packages are all from random places on the Web and were installed manually, or are from repos that are no longer available or not available for RHEL 8, then yes, you'd have to go and manually track down the packages on the Web and see what needed to be done. But with any luck, you can set up the same repos on the new and old servers, and compare their package set side-by-side as described above.
Hope this helps ! If you have any further questions, let us know and we'll see what more we can do to assist.