How to mark nodes as tier 1,2,3 etc...

It can be done, but there are multiple ways depending on the level of effort ...

a) you mcan manually update each backup client node with a custom attribute of "Tier" and its corresponding value, then you would create a custom report using the "Node Attrs" datasource to expose that attribute into a report, then create a View with a Query Node based on that custom report.   The effort here is high mainly due to creating and maintaining the Tier attribute per Backue Client

b) if the number of backup clients in your environment is quite small, then you can put the list of clients and it's tier level into a csv file then do the same steps above, custom report to read csv file, View and Query Node to that report.  This way the maintenance of the csv file is much easier than updating Backup Client Nodes.

c) the most elegant and efficient way is to have this Backup Client and Tier information in a database (eg. a cmdb or asset management database) that already exists in your environment.  This way the Client and Tier information is kept up to date by the cmdb and you don't need to maintain it.  It would be similar to (b) above except that you would create a custom report that uses the "Database Query" data source to access the data from your cmdb (or equivalent)

HTH
-E