Which 'pusher' propeller aircraft have been used in active military service?
If you also count drones, the General Atomics MQ-9 Reaper Drone is a pusher propeller aircraft in active service.

Here are some others:


Convair B-36 Peacemaker
Vickers F.B.5 "Gun Bus"
Airco DH.2
Curtis Model E
Royal Aircraft Factory F.E.2
Royal Aircraft Factory F.E.8
Voisin III Bomber
Boeing GA-1


You may notice that a lot of these aircraft are very old designs. The problem is in 1914 the US Army (there was no US Air Force yet) banned pusher type aircraft after a number of pilots died in them. This mentality carried over on the other side "of the pond" and very few pusher type aircraft entered service after 1916. The SAAB 21 was responsible for the development of ejection seats because a major problem with bailing out was hitting the propeller. Because the prop was behind the pilot, bailing out meant getting pushed through the wood chipper...

The B-36 is a good example of this configuration in its limits. It is a massive aircraft with a 19 foot propeller (second largest propellers in use). Engine fires were common due to mounting the engines backwards and not getting sufficient heat over the carburetors. The aircraft was later modified as the XB-60 with swept wings and 8 jet engines but was inferior to the Boeing XB-52 (later becoming the B-52) and was abandoned.

The other problem is that a pusher type design contributes a lot to the drag of the aircraft and is relatively inefficient compared to tractor designs. By the time swept wings were in fashion (mostly because jet engines pushed speeds higher and higher),  the need for propeller driven military aircraft dropped dramatically in the jet age.