First of all a DPC below the air brick is below ground and is thus useless.
This demonstrates how lacking in knowledge the site manager is and why you and at least 10 other properties have the same defect.
As it is, what will happen is when it rains is water will get in under your suspended floor.
That is why all air bricks must be at least 75mm above Finished ground level to the bottom of the air brick and the site manager should know this. The external wall dpc must be at least 150mm above FGL. This is stated in BOTH the building regulations and the NHBC warranty standards.
The solutions are:
1) Cut out all air brick and position them higher. But it will still mean the dpc is at the same level as the finished ground.
or
2) Lower the finished ground level around the home so it complies.
Please do not allow the site manager to give you anymore bull**it!
You may like to get the other shared ownership party involved.