I personally think no. He has similar height and head size, but for a few reasons I think no.
Firstly, he has blue skin. Thats a pretty big warning sign.
Secondly, while they share head and body structure, kaos has a unique pouty mouth and large jaw, as well as a very pronounced brow. Blastermind on the other hand has a kinder, more compassionate face. In his figure hes serious, but in game his definitely a fun loving guy, who naturally smiles all the time, with all the oposite features to that of kaos, who is always brooding.
Finally, kaos has the powers of a portal master, whereas blastermind doesnt. Portal masters have teleportation powers, and the ability to turn living beings to toys and vice versa. Blastermind is a powerful magic skylander, but nowhere near portal master level.
I personally think that blastermind is a young adult who attends a skylands college, and is a member of the colleges hide and sheep team. The uniform he wears as a figure is the hide and sheep uniform, and his crystal hat was originally a helmet. What do you think?