I do think Leon holds the BHB in special regard. I believe thats why Lowell had such a reaction to learning Dexters identity even though just moments before he had completely accepted his fate and imminent death. But while Leon probably has great interest in the BHB, doubtful that would want him hunting other members of the group. So while he might be Leons White Whale or something similar, hes still going to view him as a threat.