What exactly "snmp-server user ... remote <ip>" is used for?
Does it have something to do with sending SNMPv3 traps/informs?
With an inform, it's the manager whose engineID is authoritative, so it will be the manager's engineID that is hashed with the remote user, and sent from the agent to the manager. In this case, with net-snmp, you would create a new snmptrapd user tied to the manager's local engineID:
createUser informUser MD5 informPass123