When I analyzed bicyclist use of freeway shoulders for Arizona DOT a couple decades ago, wind blast from passing trucks was identified as one of the concerns; however, my recollection is that none of the (very few) crashes that occurred on freeway shoulders directly involved wind blast.
The current edition of the AASHTO Guide for Bicycle Facilities mentions wind blast effects on bicyclists, and recommends adequate usable shoulder width (e.g. not occupied by rumble strip or debris) to mitigate by lateral separation.
I've ridden a number of freeway shoulders, including fast downhills such as I-17 north of Phoenix, and in my experience wind blast is an annoyance but not as problematic as surface conditions, debris, or changes in usable shoulder width.