The 26-year-old returned from shoulder surgery just over a fortnight ago to touch down a superb solo try which helped Glasgow nail down a vital victory over Italian side Treviso.
Van der Merwe was at it again last Saturday when he notched another fine individual effort as Warriors bulldozed their bogey side Connacht to nail down a RaboDirect Pro12 play-off semi-final against European champions Leinster at the Royal Dublin Showgrounds on Saturday might.
And Kellock has no doubt that Warriors can reap rich rewards from van der Merwe's timely return to the fray after a season spent on the sidelines.
Kellock said: "To have DTH coming back into things just a couple of weeks before the play-offs has been perfect timing for us. You saw from the try he scored against Treviso, and then the touchdown against Connacht, he just has that X-factor.
"DTH is just a natural finisher and to have him coming back in at this stage in the season is like us having made a major inter-national signing.
"Not only has he given us all a boost by his return from injury, the great thing is that he is rested and his body is fresh following his spell out after surgery.
"I think what was obvious in both the tries he has scored in his two games back was just how hungry and determined he was to make the whitewash.
"DTH is a strong runner and he runs great lines and, once he gets going, he is a tough man to bring down for any tackler.
"But he is also a proven international and a man for the big occasion, and they don't come much bigger than taking on the European champions in their backyard for a place in the Pro12 play-off final."
So pumped up are Warriors for the Dublin date with destiny that Kellock admits one of the major problems in the build-up to Saturday night's game has been to stop his cohorts taking too much out of themselves on the training ground. The Glasgow captain said: "This is the culmination of a season's hard work for us and the ultimate test of the progress we have made. It just doesn't get any harder in European rugby and obviously the boys are up for it."
He added: "Everyone wants a jersey for Saturday night and, as a result, the lads have been throwing themselves into training.
"But it will still be important for us to ensure that we do not leave it all on the training ground. There will be a sell-out crowd of 20,000, the game is live on TV, and it is a match we are all desperate to play in, but it is vital that we save our best for Saturday night.
"We will travel to Dublin determined to execute our game plan and produce the type of disciplined, focused display we need to get the win."
Wales defence coach Shaun Edwards is to join the London Irish coaching staff after the Grand Slam winners' summer tour to Australia.