Unlike telesquirts skybooms actually have something you could call a hydraulic ladder ontop of them so i think this discussion might be a little bit more on that thin line everyone is looking for as to if its more of an engine or a ladder. Below is Wilmington Fire Department DE Skyboom 2 credit for the photo to "Lou Angeli".
I agree with the above that it would all depend on what role they are playing in that department. A town near me has what they call pumper ladders that depending on the box either respond in a truck role or as a first due engine company