In which partition did you install RHEL?
There is a problem with RedHat based installers. These installers don't detect other installed Linux distros. You have two options now.
1) Mount / partition of SuSe in RHEL, copy first title block ( first title, root, kernel and initrd lines ) from /boot/grub/menu.lst file and paste in /boot/grub/grub.conf file of RHEL. You don't have to re-install SuSe boot loader.
2) Re-install SuSe GRUB and copy title block of RHEL from its grub.conf file and paste in SuSe's menu.lst file.
If you want to re-install GRUB of SuSe, boot up from SuSe installation CD/DVD, select Recovery and execute this
Code:
chroot /mnt/sysimage
grub-install /dev/sda
exit
exit
First method is better than second, imho.