Gamma Burst’s description says “deals bonus radiation damage when the pet attacks”. It normally does this by adding a second hit that deals 75% of the damage dealt as radiation. However, attack commands from multiple pets did not ever show bonus damage being applied.
Video evidence showing the Great Horned Skag. 00:37, 00:44, 00:54 show the skag performing an attack command and not receiving bonus damage.
Gunslinger Jabber also didn’t receive bonus damage from Gamma Burst. 00:58, 01:59, 02:43, 02:50, 03:27 (the extra hit was fire damage from the terror anointment, not Gamma Burst)