Although it is highly unlikely we will recieve an essay question focusing solely on characterisation, remember that even if we do our core topic is IN THE WILD. So any notes you may have already gathered which deal with the depiction of the natural world and humanity are completely relevant - as the underlying message is communicated to the responder through the use of the characters.
Any essay question we recieve, will deserve an answer inclusive of the importance of the characters for their effecitiveness in exploring the relationship between humanity and the natural world. These texts are dystopic for their bleak outlook on the 'possible' future if we were to reduce ourselves to a life of uniformity once we become completely dependant on technological advancements.
The characters of both texts each reflect these values in different ways. If there was to be a question based on the characters this you would still talk about the themes displayed in both texts, but you would back up your statements with reference to important characters such as The Director, John The Savage, Tyrell, Lenina, and Roy Batty (these are the characters i focus mostly on in essays).
I don't tend to link characters with Brave New World to the characters of Blade Runner for i believe that it's the underlying message and the themes of both texts which link the texts themselves. I usually make a statement about the texts and then back it up with a quote from both BNW and BR to further prove and emphasize my point...
Hope that helps a little!
Good Luck!