The OG crosspicker in terms of introducing roll patterns to bluegrass guitar was George Shuffler, and he played this way. I’m told Clarence White, another bluegrass hero, was also a DDU player, but I don’t have any footage of this.
One functional difference between that method and pure alternate, for roll playing, is that the first downstroke usually rest strokes. This cuts off the sound of the middle string of the roll. You can hear the difference if you A/B this with pure alternate.
Another difference is that you can’t string skip this method between the first two strings, since they are swept. To break those apart, you’re just doing repeated downstrokes on different strings, a la Eric Johnson’s “bounce” technique. Which is mechanically the most un-economical thing you can do.
Even then, I would say there is not a huge “economy” benefit to sweeping two strings of a three string roll. The pickstroke that plays the middle note and then the high note is still going to have to go airborne in fully escaped alternate picking style, so you’re going to have to learn that movement, whether you like it or not.
Ultimately, if this works and sounds good for what you are shooting for, no harm in using it!