It seems Baron Rivendare does not trigger additional bombs from Kaboom Bot.
In a game I was spectating, there were 3 Barons on the field (one spawned from Sneed’s), but only 4 bombs spawned from the golden Kaboom Bot. This was pretty impactful in this instance, as 48 uncontested damage was lost out on.
This happened throughout the entire game, even when there was only 2 Barons on the field.