Think about this for a minute.  Besides the risk of spreading diseases; which
colonies are going to benefit the most from open feeding?  If you have a yard
with some hives stronger than others, you ought to be bringing the weaker
ones up to par.  In open feeding, the stronger ones, those needing it least,
are going to be the ones to profit the most.
As far as the spread of diseases/pests, I don't know if it's documented, but
common sence indicates that it sure would increase risk.  Personally, I'd
advise against it.
Bee well,
Ed Levi