I've been inside a Japanese ambulance!
They have loudspeakers where the driver announces that there is an ambulance approaching an intersection and for other traffic to please yield. Of course they also use the siren, but they politely ask drivers to give way as well. And I've never seen a Japanese driver obstruct an emergency vehicle; but admittedly I haven't driven much in Japan.
My brother who's a RFS volunteer has told me that he's had drivers obstruct his fire engine when he's had the siren on.