As to radio signals, there were intercepts of the Japanese warships calling up oilers for refueling, fleet maintenace signals that were intercepted.
Roosevelt arranged the Pearl Harbor attack as surely as Yammamoto. What he did not anticipate, is that the Japanese would do such a fine job.
Regards.
I believe the oilers were in company with the strike force, therefore there would have been no need to call them up. In fact the only concerns about refueling were weather related.