This has been mentiponed on another thread as well. (Not seen the magazine yet so I don't know what is being suggested exactly).
There are two concerns I guess, 1) disease transmission and 2) robbing.
1) It's possible for disease/varroa to be transferred from bee to bee, with many bees at the same food source.
2) As for robbing, I have seen it when I have accidentally left something sticky outside and near a few hives, (or leaving the bee shed door open is a good one), that there will be a lot of activity around the entrances of all the hives in the apiary as bees search for food (at a short distance the round dance does not give enough information for the location of the food source, so the bees search anywhere until they find something). So it is possible that a weak hive could be robbed - especially at certain times of the year when there's not much food about and there's a lot of bees.
So my own conclusion is that there could be an issue, but fairly unlikely.
May your bees read the same books as you do.