Must've missed that one, but I'll take a stab on lightning in hurricanes in general.

Lightning is caused largely by charged particles aloft...sometimes ice content can be used as a good marker for lightning ability. It's rare with tropical cyclones to see the necessary conditions for lightning due to low ice content and the like, but with the cold convective tops found with Dennis, it's not out of the realm of possibility to have seen some. Most tropical cyclones do have *some* lightning, just not a lot.

I'm not as familiar with lightning processes, however, as with other aspects of the field, so perhaps HF or someone can add in more.