I personally never use a retrostat with dragons, I prefer the heat light to be on all day. If the reto is set up proper then yes, it will shut the light down at a certain temp then click back on when the temp lowers some.
There is some concern that a dragon looking directly at a UVB can be bad for their eyes and having another bulb on will reduce the chance of damage. Is there any reason you are using a retostat instead of letting the bulb burn all day?