is it possible to hook up a swash plate servo to the gyro to check and see if the gyro is working properly?, my tail servo stopped working right before that the tail started jerking really bad.

In some cases, yes.

What gyro? If its not one of the newer short pulse units like a Quark, Futaba 520 or VBar, then yes you probably can.

kds 800 gyro and kdsn590 digital tail servo, the gyro has a digital on/off switch and the swash plate servos are analog

set it to analog and give one of the other servos a try

Sounds reasonable