We have a number of non pooled search heads and are contemplating making them search peers to our main admin search head. The primary use case is to support REST commands on things like saved searches, user permissions, etc that we can run within the search bar. The concern is the implication of general searches from this admin box (light use) on the downstream search heads. At some level I wonder if it would simply come down to the number of cores on those systems.
You want to be aware of load but in general this should be possible. There are cases that will break. (Notably this is not a supported configuration with Search Head Clustering in 6.2) This is however how the DMC app in 6.2 works.