You can operate a switch with a servo, but not really sure that helps you here or what it would be for. The ignition kills do not need a servo to operate.

Now that your servo is going the right way, you can use a Y harness there. I would use a manual choke cable so you can prime your engine to start it.

I would also recommend an optic kill for your ignition. Then you can kill your engine, and if you have a radio issue, the optic kill will auto shut down your engine.