In this situation, is it allowed to drive any vehicle directly behind the emergency vehicle?

In the picture there is a roadway with three lanes in one direction; the vehicles have formed an emergency corridor between the left and middle lanes, along which an ambulance with its blue lights and siren on is driving. Not every vehicle is allowed to drive directly behind the emergency vehicle (with flashing blue lights and a siren). The answer is: no.

The Road Traffic Act prohibits the driver of a vehicle other than an emergency vehicle from using the passage for an emergency vehicle formed by vehicles pulling over to the edges of the lanes; the driver may continue driving in the lane they were in before only after the emergency vehicle has passed. The only exception is vehicles of road authorities and roadside assistance taking part in a rescue operation. So driving right behind an ambulance is a petty offence, not a clever trick: the corridor must stay clear for further emergency vehicles - an ambulance is often followed by the fire service or the police - and a driver right behind it blocks their way and also risks crashing into an emergency vehicle that brakes suddenly. The correct way: you wait at the edge of the lane until all the vehicles with blue lights and sirens have passed, then you return to your lane and move off with the rest. You are also not allowed to use the corridor to get past a traffic jam.

Legal basis: Art. 9 para. 3 and 4 of the Road Traffic Act (Prawo o ruchu drogowym)