The gateway certificate should not be causing issues connecting unless you had been using an internal name for the CSA on the core side. If you were using a different internal name you will need to match this to the name in your third party certificate or else we throw a certificate error on the core. I would login to the CSA and ensure your core server shows active connections under Reports> LANDESK cloud services appliance connection table.
If it doesn't go to your core server and review the brokerservice log to determine the reason it isn't connecting.
You need to make sure you are using the exact name listed on the third party certificate