In this study, the honey stomachs of bees being fed granulated sugar were analyzed. They then established the extent to which bees dilute the grains with water on ingestion. These bees also stored the diluted mixture in cells so I think it's more than likely that feeding granulated sugar to bees during honey production will result in some percentage of altered honey. I can't imagine that there's a finely calibrated on/off signal that would facilitate the exact separation of nectar collection and sugar consumption. Testing for sucrose signatures in the honey would be the only way to tell. 



Dilution by Honeybees of Solid and Liquid Food Containing Sugar
J. Simpson  1964

https://sci-hub.tw/10.1080/00218839.1964.11100080

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