Hi,
Any SDK call for the admin plugin to know is it running in the master or slave site?
Using Milestone Federated Architecture you will set up parent and child relations between XProtect sites. Unfortunately it so that when you are in a admin plugin it has no concept of being a member of a federation. So the answer is no.
If your plugin has some relation to cameras, you will need to run the plugin on all sites and store the plugin configuration for each site. When using the configuration in Smart Client or elsewhere, you can then load this plugin configuration from each site as needed.
This will enable operators that login to the top site to see everything, while operators that login to a regional site can see the regional site and any sub-sites.