I've tried to use UNetBootin for it but Sometimes UNetBootin doesn't exactly work right and I run into issues with the BIOS recognizing the bootloader on the USB.
Can anyone recommend programs for this?
If you're on a PC, you need to use a program called iBoot (google for it, since I can't give you a link. Look for TonyMacx86's blog). You can put that on a USB, possibly, with Unetbootin alongside of an ISO of OSX...I'm really not entirely sure about USB booting since I used to try this with a DVD.
In a nutshell, if on a PC you'll need iBoot in order to even boot into OSX from the disk. I'm not sure if you can put both on the same USB, but it's worth a try.