[@Combo move] Kinda. From what I have seen, WW2-era jets along the lines of the Messerschmitt Me 262 or the experimental Flying wings (Horten Ho 229, etc) are allowed. The jet fighters seem to be Yllendthyr's (Elf empire) speciality, though other nations can have them I think. 

Overall, the RP is essentially WW1/WW2 dieselpunk "Wunderwaff" technology set with fantasy species but no actual magic (though lots of pseudoscience).