Is it feasible for SapphireIMS to detect a new device which is getting connected to their network automatically?

Yes, it is feasible. There are two ways it can be discovered.
Agentless mode: If the discovery rule is configured with a range of IP using IP Range, CIDR or domain discovery and if new device configured IP falls within the configured discovery IP range specified under discovery rule along with if it matches the credential configured for connectivity, then you should be able to discover the device. There are other conditions such as the new device should be pingable, new device OS template should be available within repository and discovery schedule should get triggered when device is connected to the network.

Agents: If new device is of type Windows/Linux/MAC and agents are getting pushed to new system by automated means such as active directory push/SCCM or SapphireIMS agentless push with right credential, then such machines can be discovered provided device OS template is available and agent deployment condition is met such as installing agents on machine reboot, machine should be available during schedule time.