RH7 is well depreciated by now. Unless you have a compelling reason for sticking with RH7, you should seriously consider an upgrade. (FC4 comes out soon! FC3 probably suports your drive right off!)
Note: DELL supports RHP9 and RHAS2.1 for this product.
SCSI tape drives are normally found in /dev/st0 or /dev/nst0 (if it's your only drive.) But DELL says the PV112T is a drive enclosure - "capable of racking up to two tape drives in parrallell using SCSI interface" While other product sites insist that it is a tape drive itself. (Presumably the enclosure would be commonly sold with a drive.) Whatever, this is SCSI, so you should be able to get it going.
You could go blindly by using tar to attempt to write to each of these devices and see if anything happens.
tar zcvf /dev/st0 /etc/X11
You could look through lspci - see if it is listed. Another trick is to use cdrecord --scanbus (which lists scsi id tags for everything scsi or scsi emulated.)
Dmesg should also see something. Look carefully - there's lots there.
/sbin/lsmod should give you a list of (driver) modules. If everything else is fine, you want to check you have the drivers.