Yes, the CD should be bootable. However, many have had problems with not booting. I recommend using Smart Boot Manager on a floppy disk. It ahs worked for many. It is available for DOS or Linux.
If you didn't see any menus pertaining to lilo, then you could try running them again from the setup program. Did you try the liloconfig command? It doesn't do anything on my installed system but it is a large script file that I think is what the setup script runs.
Now the Slack 8.1 iso image is 673,248 KBytes. Many have had problems here as well. It will not fit on a 650 MByte CDR. It requires 700 MByte CDR unless you reauthor stripping out about 30 MBytes or more of something. If attempted and the burn even completes, the result will be a corrupted CDR with missing files, etc.
You can validate the slackware directory by using the md5sum command. Mount your install CD,
mount /dev/hdd /cdrom
Note: use the correct device for your CDROM drive. Then,
md5sum --check CHECKSUMS.md5
It will process the file and verify each of the packages. It will report any problems and display a summary when finished. If you switch to another console, you can check for errors, etc using the dmesg command.
Good luck, I need to retire for the day because I need to go to work early tomorrow. But I will check back here in the morning.