Yes, they can. This does not provide any advantage on the road and only serves to attract attention. For example, in a convoy of children's buses.
If there are flashing lights and a siren, then according to clause 3.2. you must skip. Give up your lane for overtaking, give priority at an intersection (except for intersections with a traffic controller), stop if the road is single-lane. You are not obliged to violate, for example, drive to the side of the road, under a sign, into the oncoming lane, etc.
When I was little I fell on my back from a great height. So when the ambulance drove me, she used flashing lights, but no sound. When the parents asked why, they answered without a sound: "In order not to scare the child."
And perhaps this is correct. I had a suspicion of a severe spinal injury, I was transported on a rigid shield so as not to cause displacement. And if something scared me then, I could turn around and this may cause complications.
Very serious diagnoses were not confirmed, but precaution did not hurt. Escaped with a severe concussion and a compression fracture of the spine!)
According to the rules of traffic rules, the included beacon allows you to ignore some rules, but not those that can create an obstacle to other traffic participants. And if the beacon and the sound signal are turned on, then the vehicle must also let other participants in the movement and give it an advantage, even if it contradicts the traffic rules, within reasonable limits, of course.
Beacon, warns other drivers. While both signals, a beacon and a siren are a requirement for other drivers to give way. More in traffic rules.
Several years ago, an internal order was issued that the rotating beacon must be turned on whenever we go to a call, without exception. Even if it is not an emergency call and we are not in a hurry, we must still drive with the flashing light on. Sometimes it is even inconvenient: people see the light bulb is on and start letting us in when there is no need for it.
As for the sound signal, we are not afraid to use it, we just leave it for those cases when we really rush to call. I'm talking about emergency calls: traffic accident, fall from a height, railroad injury. But such, fortunately, no more than 20%. And the rest of the challenges - we are performing the role of such a polyclinic on wheels. We are going for the fifth time in a day to my grandmother, who wants her blood pressure to be measured. I will not turn on the horn, drive the red and risk for such a call.