BTW, when you install crank arms there can be spacers that apply preload on the bearings. So you should be able to apply preload with almost any crank design. For Shimano Hollowtech its like preloading the headset. You install bearings and any needed spacers (I don't think I have any in my setup, btw) and then you use the plastic thumbscrew to gently preload. Then you tighten the NDS crank arm.
That said, note that in the Timken graph below, the service life difference between no and light preload is minimal. The big hit is if you over-preload, which is easy in DGRs. But the graph below is why I suggest that you 1) snug up the bearing, and 2) apply just a smidge of preload. If you're off a bit, it ain't no biggie.
