In the rare case a PGA Tour event needs to be shortened from 72 holes, the Tour will try to do everything in its power to make sure the tournament goes 54 holes, or three full rounds. When they do that, the results are considered official for the record books and it's the closest they can come to completing a regulation event.
However, in the rare case that the weather conditions are so poor that they can't get in 54 holes, the PGA Tour strives to finish at least 36 holes. In that case, the PGA Tour doesn't consider the win official, but it does pay out the prize pool in full and doles out FedEx Cup points like normal.
For DraftKings daily fantasy golf players, a shortened tournament doesn't mean that their games are cancelled or suspended. Instead, DraftKings clearly says in their rules that they will recognize the results of any event the PGA Tour deems completed.
"If the PGA shortens an event for any reason, then the statistics that are generated for the portion of the tournament that has been completed will be used to finalize and payout contests," is the wording used in their PGA Tour contest rules.
So, if the tournament is declared official after 36 holes, then that's the basis on which they'll pay out. If the tournament goes 54 holes, then that's the stats that will determine the winners of all games for that week.