Not quite sure what to tell you. If you can SSH to it from your server that is hosting NCM and you have the profile set up correctly, it should work just fine. "Connection Refused" acts like there is a access-list or something preventing the communications.
Just to make sure, you only have the one solarwinds server, no additional pollers or anything that might be assigned to poll this node? If you did have additional pollers you'd need to make sure you could SSH from all of them.
If everything checks out, I'd probably open a ticket with SW. They'll probably want to do a webex session with you to figure out why it is this way...
