Are you concerned about losing some of the travel of the rear shock, or as to how strong the bolts themselves are? I just received my springs and drop bolts, and will be installing them soon on stock Nivomats rather than going with the lowered part number unless someone can convince me otherwise. I'm pretty confident in the drop bolts themselves - they're just a longer bolt and a spacer. I can't see any way that it could be less durable than stock.
If you get appropriate sized grade 8 bolts or stronger, it should be no problem. Loads of guys on here have done it without issue although I seem to recall a risk of grinding the shock against the rear control arm if you lower more than approximately 2".