Personally, I would be doubtful about adding croccante to a tiramisù. Croccante is generally VERY crunchy, and its texture clashes too much with the softness of tiramisù. If the worst comes to the worst you can crush croccante very finely and use it as a topping, but I think that the best topping for tiramisù is the "normal" one - bitter chocolate leaves or powder.
On the other side, I think that powdered croccante is perfect when incorporated into a parfait glacè...but the very best dessert containing croccante I have ever tasted in my life is the "Torta 2000", a creation of the genovese pastry shop Tagliafico (I mention it although it's doubtful that anyone of you will take a flight and pop over to Genoa to taste it;) )
It's made of a bottom layer of hazelnut croccante, a middle layer of a kind of chocolate genoise and a top layer of gianduia mousse, surrounded with a white chocolate leave. It's a real symphony!