I tried to use the SSL Certificate Sensor BETA in a device template. After creating a new device (a website to monitor) with this template, the certificate shows "0 days to expire". Creating a SSL Certificate Sensor without the template and with the same website, days to expire show the correct amount. Also I noticed the Settings show different menu items. Here are two images from the same sensor, the green one is created from scratch, the red one with the template: http://imgur.com/a/g57WV
I know this is a BETA sensor and probably not supported, but I thought you might be interested in this behaviour.