Goals are all scored with the puck in your possession. There are lots of players with blistering speed without the puck that never stuck in the NHL or they are checkers. Straight speedskating is good for looking impressive when you are beating out icing calls but except for the rare breakaway opportunity you need the speed carrying the puck through obstacles more. Most of the time when players get beat going back on defence it is because they were out of position or reacted late.
I would be a little concerned if a player was substantilly slower than the rest of the crop though. That would only show up more against the higher level of NHL competition but it depends on how significant the speed difference is. A player like Jason Allison, who's lack of speed almost negates his high skill level and huge stature, is probably .5 seconds slower in a dash type drill than a player like Brassard, so Derick might be nowhere near slow enough in the dash to hurt his chances in the pros. You would need to be able to compare these tests against current pros or ones that were the most extreme examples of these skills. like Denis Savard carrying a puck through obstacles. Some of these numbers on disappointing draft picks like Doug Wickenheiser, Ken Yaremchuk, Pat Peake, or Alex Daigle might be really enlightening.