The fireplace needs a simple dry contact closure so any type of relay will work. It can be a very small relay because there's hardly any current involved. You don't even need the Control4 switch if you have any Control4 product with dry contact outputs.

The fireplace gas valve is turned on and off via a thermocouple which gets its electricity from the heat generated by the pilot light. If you didn't know any better it almost looks like magic.

Ernie, please weigh in if I got any of my terminology mixed up.