How did the recording engineer achieve this effect on the drums?

The best tape flange effect I have ever heard/seen demonstrated in a DAW was in Craig Anderton's video SONAR X1 Advanced Workshop: The Next Level. I do not believe the video is available but Craig updated the process to use Aux tracks and included a description of it in his "The Second Big Book of SONAR Tips." I checked and Craig's "The Huge Book of Cakewalk By BandLab Tips" still contains the chapter. The pdf is on sale for $20 and contains a lot of useful tips like this one.
 
With permission of the author here is...

The Gourmet Flanger
 
I’m always looking for ways to get the “tape flanger” sound of “through-zero flanging” without tape.
The differentiating aspect of through-zero flanging is that when the delayed and straight signals are
out of phase and at the same delay time, they cancel to create a split-second of silence. Although the
Sonitus Modulator offers a Tape option that approximates this sound, you don’t have control over how
the Tape option works—with real flanging, tape motion was always somewhat variable; more often
than not, the tape would sort of stagger around the through-zero point. So can we get an even more
realistic tape flanging sound with SONAR? Of course we can!
 
The setup is a little complex, because we need to take the audio we want to flange and send it to two
buses, or the same Patch Point in two Aux Tracks (as in the screen shot below). Note that with Aux
Tracks, Input Echo needs to be enabled. Each Aux Track has a Sonitus Modulator effect, with one set
for a constant 0.1 ms delay (labelled as the “Reference” track, which is also set out of phase), while
the other “Flanger” track is set to sweep so it goes up to a lesser amount of delay than the zero-
crossing point (in this case, 0.01 ms). Therefore, the signal cancels once when it sweeps up through
the 0.1 ms delay point, and again when it sweeps back down through the 0.1 ms delay point. You want
the interval between these two times to be fairly short; however you can lengthen this by increasing
the Reference track’s delay parameter.
 

 
Set the Mix controls to 100% delayed signal for the maximum effect. The Flanger track’s Depth control
determines how low the flanger goes. 3-5 ms seems about right, but feel free to increase this for a
wider-range effect that gets more into the chorus/delay range. Also, try different LFO waveforms. My
favorites are the Triangle and Peak / Dip waveforms.
Turning off the Phase button on the Reference track produces a different timbre that’s also useful, but
the signals don’t cancel at the through-zero point, so they create a volume increase. In that case you
might want to lengthen the Flanger track’s Delay parameter to avoid the through-zero point. I prefer
the out-of-phase sound because it sounds more like “classic” flanging to me, but at least you have
options. You can also experiment with increasing the amount of feedback; just remember to keep the
levels identical.