Yup, I do it all the time. All of my servers have onboard SCSI for their hard disks, and the ones that manage tape drives/libraries all have an additional SCSI controller for the backup device. This is mainly because the tape systems have different interfaces/connectors/modes than the onboard controllers, and the fact that we want the backup device to be on a separate channel/bus for maximum performance. As long as you stick with the more "brand name" SCSI controllers, you shouldn't have any issues with drivers interfering with each other.