I have this scenario of patchin RH AS 5.2 servers, please let me know if this is possible.
Server is at 5.2 and I need to update this to 5.8. I can't go beyond 5.8 due to application restrictions.
Given that scenario, how can I download 5.8 with the latest errata? Also how can I keep track of these errata's that is getting released on 5.8? Meaning 5 months down the line if I have to patch that server with all the errata's that was released between now and then how do I do it?

Red hat provides an ISO image of 5.8 but that's only the base image and it doesn't have the latest errata's in it. Any idea how I can achieve my goal?

RHEL 5.8 with the latest errata *IS* RHEL 5.10. The minor versions are really just update baselines. What is this application issue you refer to?

What advice did RedHat give you about what you're trying to achieve?

In 5.10 it becomes a different kernel isn't it? Lets say we just skip the kernel alone and apply all other rpm's from 5.10, wouldn't it complain of kernel dependency?

I have opened a case with RH, they're yet to get back to me.

Certain version of SAP is compatible at present only to that level of RH

I'd suggest asking SAP WTF you're supposed to do personally. Christ I hate SAP. Are you sure it wasn't just the latest release of EL5 at the point they made the compatability notice? By definition, Redhat EL5 should run all apps the same way, no matter what patch level it's at, save for bug / security fixes etc.

As far as kernels go specifically, it'll still be 2.6.18. I can't see a quick list of ALL officially released EL5 RPM's from redhat over the last however many years, but there will have been well over 100 I'd say, far more than the actual number of 10 minor release numbers, each one just fixing bugs and improving stability. it should still work the same.

And you wouldn't be "applying the updates from 5.10". You'd be applying the updates to EL5.