There is nothing in the expression "fire off" to suggest the intent, or the lack of intent, to hit a target. However, that suggestion is carried elsewhere in the sentences you cite. A "warning shot," for example, is just that: a shot fired off to warn an adversary or threatening other against persisting in some action. Warning shots are aimed away from people (often times over their heads) as a means of intimidation. Likewise, shots fired off in celebration of an event are not intended to do damage--they are intended to create noise and merriment. These are usually shot into the air, with no intent to hit anything.
However, in your middle sentence, "They fire off a volley of shots," there is no indication of purpose or intent. It may be that this volley of shots is directed away from people, it may be that the shots are intended to kill, or to hit some other target.
In other words, you need more context to determine whether "fire off" in this sense indicates a desire to hit a target, be it animate or inanimate.
See this, from news reports:
From 1970 to 1975, the British military fired off 55,000 rounds of
5.9-inch (15-centimeter) rubber bullets in Northern Ireland, reportedly killing 13 people at a death rate of 1 in 18,000 rounds and
resulting in a severe injury rate of 1 in 800.
Clearly, the military fired rubber bullets intending to hit their targets. It may not the case that the bullets were intended to kill--theoretically, they are designed not to kill--but they were fired off explicitly to inflict pain and to disperse crowds or otherwise disarm/disable the target.