I spoke with a buddy of mine at USFWS about DNA in cases. Granted, this case is not a USFWS, but a Utah case, however I doubt the procedures necessarily vary that much. Basically, he said that they did DNA even prior to having suspects or warrants depending on the seriousness/priority of the case, which I found interesting given the time and effort involved. In fact, he said they may do whole workups on DNA, serology, hair, feathers, hide, etc. as needed even before there is an actual suspect if the case is assigned as being high priority.
Determining priority can depend on numerous factors. Certain types of animal cases often take precedent over others, such as if a lot of carcasses of animals are found or if the animal is a high status animal such as a bald eagle that has been shot. Then there are the aspects of the investigation such as if the animals are potentially linked to a larger or ongoing case, such as trafficing in poached animal parts (i.e. bear gall bladders to the Asian market, for example).
Those which are not tested on a priority status have various tissue samples taken and stored for future testing/analysis as needed.
So did they do DNA apriori the warrant in this case? Maybe or maybe not, but they can get DNA from antler and identify individual animals. So antlers can be tied directly to the individual carcass from which they originated if there are samples of each to match.
"If you look through your scope and see your shoe, aim higher."
-- said to me by my 11 year old daughter before going out for hogs 8/13/2011