Pool with Least Sessions LB Method having 2 Virtual Servers with different persistence methods

Unless I'm misunderstanding your question, load balancing honors a persistent connection and Least Sessions (or any) server selection should only occur in the absence of a persistence record. Further, cookie persistence is, generally, based on the virtual server name, pool name, and then node/port. So a persistence cookie, if transmitted to another virtual server, should not affect that virtual server's persistence or load balancing process.