To Ichigo Kenpaichi and Hollow Ichigo are nearly the same except that Kenpaichi isn't dangerous. Ichigo knows that he needs to change and learn how to accept that fighting spirit but Hollow Ichigo scares him, he believes that if he lets Hollow Ichigo become part of his dominant personality he'd lose control. That's where Kenpaichi comes in, Kenpaichi has one of the greatest fightng spirits Ichigo knows of, yet he still maintains his group in a near fatherly matter and his subordinates seem to love him. Ichigo is using Kenpaichi as a template for the person he wants to be, someone with a fighting spirit but still in control. Ichigo saw Kenpaichi as what he would allow his new persona to be more like which explains Kenpaichi coming in a vision.