From what i can tell, when you pair the apple watch with the Tickr and they are connected the apple watch does not use it's build in sensor for heart rate measurements. If you look in the health data even after a short workout it's flooded with measurements from the tickr but nothing from the watch. I mean like 10 times a minute at least measurement wise but there isn't any data from the watch.
I just ran a quick test with mine and started a workout on the watch with the tickr paired and I didn't see the green led's light up on the bottom like I do when I don't have the tickr paired.
Also I've noticed on days when I forget my tickr the apple watch definitely takes more of a battery hit during workouts.