Well now, we don't know how a fusion reactor works, else we would be building them right now. 
And since we don't know how one works we can't say for sure what it would do if it got bombed.
's called a Tokamak. We can build them, we can even break even, we just can't do so by enough to be worthwhile. The failure mode of a fusion reactor as science understands them at the moment is not going to be a detonation. You'll lose magentic containment, the reactor plasma will get loose, and it'll burn a hole through damn near anything in the five-ten seconds before it loses all its energy. Since it uses hydrogen for fuel, if the reactor plasma reaches the fuel tanks, yes, you might get a pretty impressive explosion, depending on how much fuel's left. (Like gasoline tanks, it's the vapor form you need to worry about. That is, assuming you're using something other than the gas to store it already.)
All nukes currently in service use conventional explosives to trigger a nuclear reaction by adding the necessary heat/compression/what-have-you. However they use very safe explosives, of the kind that don't go off unless very specific conditions are met. In that case, it depends on the safety settings of the warheads. Modern ICBMs, for example, have a setup which prevents the missile from arming unless it reaches a certain velocity; until then the warhead is about as inert as you can make it. For fuzing, they use a simple VT fuze or even a timer, since most are designed for airburst. Until it arms, however, you can do all kinds of crazy stuff to an ICBM warhead, up to and including smashing it to pieces or lighting it on fire, and it won't go off. (On the other hand, I wouldn't try electrocuting it.)
With the given stuff already, I would assume that the warheads are contact-fuzed, probably with an arming timer that prevents them from arming for x number of units of time after launch; rather like a torpedo. The safety of the weapons themselves depends a lot on how they're designed to be handled and stored. If they come as all-up single units, ready to fire from out of the factory, then the safety measures will be impressive because it's
able to go off somewhere you really don't want it to. If they're designed so that warheads and fuzing systems are handled seperately until the weapon is issued for use, then the safety measures will be less impressive because the probablity of it going off before it's wanted to is a lot less.
