Limitations on how many DMCC terminals can be registered per AE Service are discussed in the "Communication Manager capacities for DMCC" section of the AE Services Overview document.
So, for example, with AE Services Profile 3 connected to a large Communication Manager using procr and no encryption, each AE Service can register up to 8000 terminals.
There is no limit on how these registrations are distributed amongst DMCC clients. For example, a single DMCC application can register all these terminals using a single connection. Alternatively, 8000 different clients can each register a single terminal.