First, that claim is patently false. Two objects with size accelerating directly towards each other (i.e. zero orbital angular momentum hence zero "orbit") will produce waves. A moving object will produce detectable changes in gravity so arguing about "waves" in the context of atomic clocks detecting gravity is irrelevant.

I don't GR but I'm fairly certain dipole does not work for gravitational waves (i.e. two objects accelerating straight at each other). Supposedly, there's a specific definition of "gravitational wave" here. You can, of course, detect the change in gravity though, regardless of "gravitational wave" or not.