So I just ran a test; 50 Ohm output set on the DG1022Z, 5 Vpp into a 50 Ohm coupler on my DS1054Z. When I went from 100,000.000,000 Hz to 100,000.000,001 Hz, the output decreased from 5.04 Vpp to 4.92 Vpp, a difference of 120 mVpp. It's a definite change that occurs at that specific point, leading up to and after the point, the voltage is steady.
There's probably some lookup table that switches over at this point but I'm unconcerned. What I typically do is set up the DG1022Z to close to what I want and then monitor the voltage applied at the point of insertion using an accurate multimeter while tweaking the controls to make sure the input is at the desired parameters.