if you want just to keep track of reachability and aliveness, then allowing PING will be sufficient.
if you'd like to collect information with SNMP, then your client system will have to run an SNMP agent (e.g. the common net-snmp daemon for UNIX-ish systems, or builtin agents on most networking or embedded hardware)
NMIS makes use of 2 technologies to monitor your network devices - ping and SNMP (supporting v1, v2c, and v3). Since SNMP ships with most devices today, it is still a service which must be enabled and managed.
Do I need to install a client component/widget on the device?
JR