The SSH Server Host Keys are used by all applications that play the role of an SSH Server. Specifically Tunneling in Accept Mode. These keys can be created elsewhere and uploaded to the device or automatically generated on the device.
While uploading existing keys, ensure the Private Key will not be compromised in transit. This implies the data is uploaded over some kind of secure private network.
Note that some SSH Clients require RSA Host Keys to be at least 1024 bits in size.