Would ground effect and FOD ingestion be factors at high speeds close to the ground? How could flight 77 into the pentagon overcome the compression lift of the ground effect at 460 KIAS that close to the ground? Also wouldn't the engines ingest FOD at that power setting that close to the ground on the approach?
The amount of time a plane in a dive spends close enough to the ground to ingest foreign objects and thereby damage its engines is of order ~fractions of a second. 

For a plane that is about to strike a building on the ground, the idea of FOD damage to its engines is not even relevant.