If I understand what you mean, I think it is not possible. The task representation (in XML) does not contain a type. In the Abiquo API, there is only a generic Task type, which has an owner (not an api user, but an entity; the task owner is the entity that "has" that task: virtual machines can have tasks, images can have tasks too, etc), and depending on that owner, the task may produce a result of a type or another (the task may produce a VirtualMachine, an Image, and so on).
This purpose of this method is to fill that gap, and provide, in jclouds, a concrete class type for each Task, and I'm doing that by looking at the owner of the task definition.