Yes you can. As long as your Ultra320 connections match you should not have any problems. The only issue is that if your SCSI controller either onboard or card based only supports up to Ultra160 transer speeds then the Ultra320 capable drive will be dumbed down to the Ultra160 transfer speeds. It all depends on what the SCSI controller supports but it will work since Ultra320 drives can run off of Ultra160 controllers.
I hope this helps.