I currently dual boot Slackware64-current and OpenBSD 6.1. Lilo is installed to the MBR. I put the following addition at the tail end of /etc/lilo.conf. This assumes that swap is sda1, / is sda2, /home is /dev/sda3, and OpenBSD is on /dev/sda4.
other = /dev/sda4
label = OpenBSD
table = /dev/sda
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