Even if you beamed a signal straight at another planet in another galaxy, the planet would not be ‘there’ when the signal got there.
i would assume anyone that’s using a gamma beam to communicate would understand, and compensate for, stellar drift during the communications time
of course, gamma radiation would be too slow to get there in any reasonable time frame.
which would leave you with entangled particles as the primary mode of communication... something we could never eavesdrop on or find evidence of