jackyga go with your gut on this one. It is definitely not a good idea to blend RCA(recycled concrete aggregate) with garden soil for use in a lawn.
The purpose of RCA is for providing a firm ,compacted base under something, as in your paving stone patio, which is something you don't want to happen to your lawn.
It sounds like your contractor just doesn't want to haul it away.
By the way, how much crushed concrete are we talking about?
ALOT doesn't really give me much of an idea.
If it is a few wheelbarrows that might be mixed in with 30 yards of garden soil I might not be "too" upset but if it is a few yards to be mixed in with a similar amount of dirt I would be adament about not allowing it.

Long story short.
Don't allow it for any reason.

Whether crushed concrete should be added to any soil depends on the soil. Maybe, possibly clay soils where it might, maybe, possible help with drainage but never in sandy soils, assuming the concrete is crushed really fine. Since concrete is lime (Calcium Carbonate) be aware that over time it might affect your soils pH, too.
Adding crushed concrete to clay soils would be like adding sand and to make a significant enough difference you would need to add a lot, like 45 to 75 percent.

"Lime, or calcium carbonate (CaCO3), is the naturally occurring mineral used to improve an acid soil. All grasses prefer slightly alkaline soils." (From wikipedia: http://www.calciumproducts.com/component/k2/item/201-difference-between-lime-gypsum . )

The modern world's soils and turf are troubled by a tendency to acidity, or low pH, due to acidic rain which comes from industrial processes and in particular coal burning power companies. To improve a lawn, calcium carbonate, limestone, is often added, likewise to agricultural fields. Crushed concrete is a good underlay or incorporated medium for a turf grass lawn. There is another benefit to crushed concrete incorporporated into soil for a lawn, and that is it is a powerful deterrent to Voles and Moles which do not like digging through sharp mediums. Have you ever noticed how well grass seed and other plants grow up in cracks in a concrete walk or drive?

Resurrecting a 6-year old thread to advocate for calcium product sales. Oooh-kay.

As I understand it, concrete may or may not be alkaline depending upon its age and how leached out it is.

Also, you should never assume your soil is acidic and add lime to it without a good soil pH test to verify. Many soils are neutral and some are already alkaline. Lime would be a detriment in both cases.