Yes, you're right the
partitioning scheme is a GUID, and that puts a ~200MB EFI hidden partition on the stick - and the
format is Mac OS Journaled.
If you used UniBeast 8.* all should be ok so it is indeed strange that it isn't.
Run Terminal with the command "diskutil list" and check it out. If your main HD is disk0 then the USB will be disk1 (assuming no other disks) The main area of that stick will show then as disk1s2 - the hidden EFI partition would then be disk1s1.
You can easily check from the Mac you created the UniBeast stick on, but I understand if you don't have a working, bootable Mac to hand this can't be done easily.
Another thing to check is, as I said previously. If your memory stick is borderline not big enough UniBeast does sometimes finish its process but the USB stick won't work. Make sure you have plenty of room. When I had this problem I pinched a 16GB SD card from a camera and used that in a reader to create an installer!
Finally, if you feel really technical check the format of the hidden EFI partition. It should probably be MS-DOS (FAT32) in most cases, as will the EFI partition on your HD/SSD.