jfs can be used for booting if and only if its grub were written in the MBR, but the same jfs grub may not work if written into the first boot sector. However if the grub were into ext2, ext3 and reiserfs it should boot with both the options.
But if the linux os is of a binary installer system such as deb or rpm, then it shouldn't matter as booting via the command configfile /boot/grub/menu.lst would bring back the menu screen the same way as a chainloader +1 would do.
Earlier in my old i586 machine I had used a jfs based linuxmint-grub to boot other operating systems (opensuse, opengeu, pclinuxos-gnome, granular), but return back from other linux's grub graphical menu to the linuxmint-grub (jfs) graphical menu via the command configfile /boot/grub/menu.lst.
Although I was familiar with the jfs boot in the MBR as a good option, I realized its inability to boot via the first boot sector's chainloader +1 only recently while trying a similar way out in my new i686 machine having sabayon, ubuntu and mandriva.