Yes, BMC Client Management manages devices through internet either through a DMZ relay if no VPN is available or it is not necessary to set up a DMZ relay. If you cannot use VPN to connect to the relays, see DMZ-architecture for more information.
If you are using a DMZ relay, you must configure the DMZ relay and its clients to properly manage unstable communications. For more information, see this Knowledge Article Client Management: Improve Internet / DMZ / VPN communication and limit "Queue Full" on Relays.
Relays support 2000 clients for Windows and 5000 for Linux. You have to configure these settings on the Linux master. For more information, see Best-practices-for-masters-and-relays-deployed-on-Linux.