Any way, the problem is solved. It was due to wrong GRUB menu settings. I was previously using EFI v8. So GRUB's OS X entry was set like this:
title OS X kernel (hd0,5)/boot/boot_v8So, as I understand now, I was trying to boot a Chameleon based boot loader with boot_v8 boot loader. No wander I couldn't boot from an EFI partition like that. Stupid me
After a long Googling session, I've found how to setup the GRUB's menu to boot the Chameleon boot loader.
It must look like this:
title OS X New rootnoverify (hd2,0) makeactive chainloader (hd2)+1Some info, just in case... I have the Chameleon based OS X installation on a separate external USB HDD. The other OS X installation is located on an internal SATA HDD. The main two OSes are located on a RAID0 disks. The primary boot device is the RAID0 massive. So the disks in GRUB's language are enumerated like this:
RAID0 - hd0
SATA Nr2 - hd1
External HDD - hd2
In hd2,0, 0 is the first partition on the diks (the second one would be -1, the third - 2 and so on).
It is very easy to setup GRUB's menu, if you only know how
Thanks to kizwan for pointing me the right direction! You've saved me a lot of nerve cels