I've been able to get multiple OSes booting fine under my system's native UEFI (also have TianoCore DUET installed but it is of limited use, mainly to work around issues, and Windows seems to have problems sometimes without it). It seems that flashing my BIOS erases/resets the NVRAM variables, also resetting to optimal defaults in BIOS does so as well. I got Fedora Workstation 22 installed today after multiple tries, I kept hitting an issue where it seems that the Anaconda installer couldn't write an entry to NVRAM for whatever reason. I think it came down to my NVRAM not having enough space for more entries, as well as duplicate Windows Boot Manager entries. I had to reflash BIOS and delete a few invalid entries with efibootmgr, which allowed Fedora installation to finish and be bootable. However, several hours later, Fedora's GRUB2 NVRAM entry disappeared, I noticed this after GRUB2 failed to come up on a reboot, and Windows loaded immediately. I didn't reflash BIOS or mess around with efibootmgr after Fedora installed, so I'm not sure what caused this. Currently ArchBang's NVRAM entry is the active GRUB2 loader, but this may disappear too.
So I'm wondering if there is a program/utility that can dump the entire NVRAM contents to a file, much like a disk image, and allow for restoring later. I'm guessing the answer is no, generally not.