As Beth said, closeness isn't important, accessability is. You need to have clear access to the rear of the hives so that you can stay away from the flight activity - the dramatically keeps you safer and more "invisible" to the bees you are tending to.
Just remember that FIELD POLLINATOR BEES are typically trucked in and lowered by lift to the pollination site and all the hives are on pallet (where they stay until picked up) this keeps them from sinking or tilting over too which is very important, the pallet works as a fairly level foundation.
The only problem (one that THESE bee users don't concern themselves with) is access. You would not want to have hives with opening facing in all directions. As we spoke last night, keeping a strong easterly lighted front is ideal, but side to side you will need enough room to safely get your hands down between the hive supers so that you can grab and lift them as needed. Otherwise, closeness isn't much of an issue.
Hives are very heavy and cumbersome - most importantly, they are a back safety hazzard if you can't maneuver them around properly. Fitting them into a tight space between existing hives can be tricky and getting hurt is pretty easy.
So plan it out for your own health issues. Literally, they could be inches apart - the bees will always find their own home and if not, the bees from the neighbor hive will quickly dispell them until they find the right one - your job is to protect yourself and I strongly suggest having TWO SIDES of access, the rear and at least one side - that way you can maneuver better without having to bump into the other colonies.