Hi,
Nagios connector are not GA (Can not download from SOI connector page).
As per my knowledge CA has internal team named Global Delivery (GD) team who had this connector developed and can be made available to clients on request (Might involve some finances too).
You can request your CA Account Manager to check this with CA Product Delivery or GD team and they will let you know all details.
As far as your questions concerns,
You should download 'CA Service Operations Insight - MULTI-PLATFORM'
Thanks,
Ashay