The real issue is - the ratio of the physical body's heat-outputting capacity to the volume/mass/insulation of the environment that surrounds the heat-outputting body.But of cource they heat the hive..........
In most all our contexts - a cluster of bees does not really heat the enclosing hive significantly, ESPECIALLY well ventilated hive (in few cases IF they do sometimes - this is not healthy or sustainable for long term - that recent video from KevinWI is an example).
Of course, any physical body that has the temperature higher than the surrounding environment is HEATING the environment due to well-documented physical processes of energy transfer - via a combination of direct radiation/conductivity/convection. This is not a special case particular to bees, but rather very general thermodynamics.
Right now I am sitting in this huge office building and also am "heating" it - however, my heating contribution to the building's heating is a virtual zero (relative to the volume/mass of the office building).
Now - IF they packed 5 thousand people on my floor - that could create noticeable heat/moisture outputs (compare that to a conditioned and insulated commercial storage packed with hundreds of heat/moisture outputting hives - the same).
Now, let us move the same 5 thousand people into the parking garage just below the building (very well ventilated garage made from concrete) - let me tell you, the garage will stay cold.
This will be a case of an apiary wintering outside.
SO - we have 1) a single hive context and 2) a large apiary context.
These are different contexts.