Hi Recarter,
There isn't any GUI way to do that apparently (afaik). However, If you are using snmpcollector 3.2x (requires UIM 8.4) you can delete the devices running a delete query against the H2 database that contains the snmpc configuration. Please, before making any change ensure that you backup your entire snmpcollector folder. I have tested this on a small subset of devices and it worked fine - However, this is undocumented and not an out of the box feature, consider it as a work around and please prepare for a rollback if needed.
go to http://<snmpcollector_robot_ip_or_hostname>:9715/database click OK without entering any password. It now connects to the H2 DB.
Run the query below to see your devices on the table:
SELECT * FROM SNMPDEVICE
Then create a delete query at your need:
DELETE FROM SNMPDEVICE where <identifying_attribute> = '<value>'
thanks,
Marco