Red Oak Grande Isle Retro Stair Tread Closed 36 in

Yes - retro treads will fit over this type of sub-tread.

The thickness of the sub-tread isn't necessarily important because you're refacing both he tread and the riser. This link has a diagram that better shows overlaying a 2x12 (1-1/2" thick ) with a retro tread:

https://www.stair-treads.com/resources/replacement-stair-tread-information.html

These treads are solid Oak hardwood with no veneers or junk filler material / plywood. We do edge glue all of our solid stair treads and other wood products for stability though. "One piece" stair treads are very prone to cupping, warping, end checking, etc. (think about the steps of a deck that are typically made from solid 1x6 pine and how much they warp and move over time).

We have a helpful article that goes in much more detail here:

http://www.stair-treads.com/faq/edge-glued-stair-treads.html