IRULE for SNI is necessary

SNI-based cert selection and pool assignment are generally two different things, so if you can do SNI at the VIP, and you are offloading SSL at the VIP, then pool selection can be based on HTTP events:

when HTTP_REQUEST {    
    switch [string tolower [HTTP::host]] {        
        "foo.site.com" { pool foo_pool }            
        "bar.site.com" { pool bar_pool }            
        "blah.site.com" { pool blah_pool }
    }
}