Rtech, I concur with Steven here; when tilling around my fruit trees I've been shocked 
at how near the surface their roots are. No doubt you'd cause some damage tilling deeper than 2 or 3 inches.
Also, frequent watering of an annual vegetable would do just the opposite of what's best for a fruit tree - deep, less frequent watering. Shallow watering would cause the roots to surface even more.
Finally, sunlight would be scarce; I can't think of any benefits - but a good brainstorm!
If you look at older farm and garden books you can see that it was usual practice to interplant between young orchard trees. This allowed the spaces between the trees and the rows to be used while the trees were growing. They usually used small fruits like berries for a quicker cash income while the trees were growing. Standard sized trees take up a lot of space and when just planted they have plenty of room between trees that the roots don't use. The planting must be done outside the dripline of the trees to avoid damaging the roots. Blueberries, strawberries or cane berries would work well and don't require a lot of tilling of the soil. They can also be watered a bit less frequently than annuals or vegetables. As the trees' dripline expands, the plants must be removed. Even dwarf trees can be interplanted when they are young as long as you stay outside of the dripline. That will keep you from drawing nutrients from your young trees and protect the feeder roots just under the surface.
In a very small yard a cordon or espallier could be used for the fruit tree and that would allow more valuable groundspace for small fruits/berries as the dripline would then take up a much smaller space.
planting members of umbellaria family (carrots, parsnips, etc.) can provide a host for parasitic wasps that attack apple maggot. I plant earth chestnut underneath for that reason. I like to eat the leaves of earth chestnut, and you can eat the bulb, although it is very unproductive. Mostly it's insurance for the apple maggot, which has never become problem with my apples. I wish it would work for codling moth.
John S
PDX< OR
chives under fruit trees are also great for deterring aphids. I've planted strawberries and chives under
peach, plum, cherry and apple with great success. By the time the trees are fully leafed, the strawberries are happy for some shade. In our large organic orchard we planted clover, alfalfa, vetch and others as green manure and tilled it under a couple of times a year.
Idyllwild
simplepress
jafar
Marsha H
Viron