There is one thing that I think would provide more weight to the "Preferred Enemy allows the reroll" point, and it is that the rule
Gets Hot and Re-rolls uses BS6+ as an example of a time when the you can reroll the result.
The wording for BS6+ says:
... it gains a re-roll whenever it rolls a X To Hit ...
Having BS6+ grants access to the re-roll. If we go with your logic as to why Preferred Enemy can't be used, then we would have to assume that the same argument would apply to BS6+ despite it being used as an example. We would have to operate under the idea that because BS6+ specifies a specific result on the To Hit roll, and that
Gets Hot for a blast weapon is not a roll To Hit, then it would not be permissible to re-roll.
Twin-Linked has also been brought up in this discussion, and it is generally accepted that it can allow the re-roll because it is used as an example in
Gets Hot and Re-rolls. But again, if you are arguing that the roll before firing a blast weapon is not part of the hit roll, then Twin-Linked wouldn't apply either.
As I have said before, the important factor is that Preferred Enemy grants a re-roll on the To Hit roll. Regardless if that re-roll is dependent on a certain result or not, it does grant a re-roll.
Gets Hot and Re-rolls' only stipulation to what qualifies a model to utilize that rule is whether it can re-roll the hit or not.
Does a Devastator (that has preferred enemy from somewhere) with a Plasma Cannon get to re-roll if he fires his Bolt Pistol if he rolls the required number? Yes. Does that Devastator have the ability to re-roll his To Hit roll? Yes. Does
Gets Hot and Re-rolls give details on how to handle situations where a model has the ability to re-roll and is firing a weapon that does not roll to hit? Yes.