The DNA digivolutions are as follows. Keep in mind that in order to do a DNA digivolution you must only have 2 Digimon in your party and in the following combinations. A very important note: In essence this basically removes your entire party then adds the DNA Digimon, so no stats, abilities, genders, etc. will be transferred. It will; however, give you a stronger Digimon in the long run, some of which can digivolve even further.
WarGreymon + MetalGarurumon = Omnimon
These Digivolutions are optionally accomplished via trading, which I will point out below:
WarGreymon(Nevermeltice)/MetalGarurumon(Dragon Fang) = Omnimon