I have found that while these two should be the same, mathematica does not evaluate them equally.
Integrate[(a + b el + c el^2) DiracDelta[u], {u, 0, 1}, {el, e1, e2}]
Integrate[ Integrate[(a + b el + c el^2) DiracDelta[u], {el, e1, e2}], {u, 0, 1}]
I believe the second one is correct...