I stand corrected.
I'm not sure, what did they trade IOTL for the plans to the Me-262 & Me-163? I think if the Japanese learn of the Do-335, the Germans would find a way to accommodate them. The Germans (even Hitler) knew it was in Germany's best interest to keep Japan in the war.
Not sure about the Me-262, but apparently the Japanese bought the license and designs for the Me-163. But yes, good point: the Germans wouldn't mind selling the design for the Do-335 to Japan if it means helping them pin at least some of the Allied forces away from Europe if nothing else.
Though, with the Ki-84 entering service by 1944, and apparently capable of mounting drop tanks, dedicated heavy fighters may not be needed. If the Ki-84 could reach and attack enemy heavy bombers in flight, they can fly escort for Japanese heavy bombers as well.