Most legal codes will specify that regrooved or retreaded tires cannot be used on the front wheels of a bus. It never specifies anywhere else. These tires are usually tires that have been cut again after the treads have been worn out. The treads on these tires aren’t inherently less than anything else. However, there are stories of retreading going wrong.
It is also a common scam. Regrooving can be a dangerous thing to do to the tires. Old tires can be incredibly worn in other areas of the tire, and not just where the rubber contacts the road. So, while the DMV may only ever specify that the front wheels of a bus shouldn’t be regrooved or repurposed, there is a reason to be weary of them.
In the Commercial Driver's Manual of NYS, section 2.1.3 Claims that "regrooved, recapped, or retreaded tires on the front wheels of a bus. These are prohibited". It does not says anything about outside dual only.