This is possible, however all minor OS revisions will be grouped together by their major version number from within HP SA.
For example, say you upload three different OS Media kits to HP SA using import_media: RHEL 5.1, 5.2, and 5.3. Each would have their own MRL that would point to the media specific to that version, but each MRL's "OS Version" within HP SA would be the same (Red Hat Enterprise Linux Server 5), which would make the "OS Media" tab look like so from within the HP SA Web Client:
Name | Path | OS Version RHEL 5.1 | nfs://mediasrv/media/linux/rhel-5.1-server | Red Hat Enterprise Linux Server 5 RHEL 5.2 | nfs://mediasrv/media/linux/rhel-5.2-server | Red Hat Enterprise Linux Server 5 RHEL 5.3 | nfs://mediasrv/media/linux/rhel-5.3-server | Red Hat Enterprise Linux Server 5
You would want to change the name of your OS Media, OS Profile, and OS Sequences to reflect the minor version accordingly, else wise you will not be able to tell them apart.
As far as the multiple initrd's aspect of your question, I don't understand what you are asking. If you are asking how does HP SA keep the packages for each minor release separate, that is done via import_media during package upload -- each package gets a unique unit ID that gets associated with the specific MRL that you are creating at that time.