Creating an alarm at a global group level applies to all groups and it subgroups as well. Similarly if you create your alarm at a top level group its applied to all it sub group as well.
In this case you can either create your alarms at global group or create a top level group and apply it.
I have grouped my volumes as follows:
Sites/<Site Name>/<Filer Name>/<Environment>/<App>
This has allowed us to easily report on these groups using OCR however it has made monitoring quite a challenge. It looks like my only options are:
I was hoping the alarm email would contain the group(s) the object (say a volume) is a member of however it does not. If you have any other ideas let me know.