When you run 1.9.5 (with Ardour 2.8.8 and Hydrogen 0.9.5-beta2 at least) you don't have to set Ardour as Master.
Without it, if I click anywhere on the timeline in Ardour, Hydrogen jumps to that spot.
It also works the other way around if I click somewhere in Hydrogen.
Yes, but then, who is the tempo master? I have an ardour song with several tempo changes I made from a tempo map with klick2ardour. I have hydrogen which follows the tempo changes perfectly but only as long as I set ardour transport as jack master. I have just tested it again with jack2. I am back to jack1.