I’ve built 3 bows made with waxed wood-turner blank risers. I haven’t had problems with any of them. The wax is put on wood that is wet to allow a very slow drying process to prevent checking. So, it does need to sit for a while before use. Personally, I let the wood sit in the garage for roughly 6 months before doing anything with it. I live in a dry climate, humid areas may require longer.
My first step when building a riser is to scrape as much wax off as possible. Then I use spray adhesive to secure a piece of 60 grit sand paper to a flat surface (I use plate glass.) I’ll run the riser over the paper to remove the wax. Initially, ever few passes will result in wax caked on the sand paper. I use a stiff steel brush to remove it then continue with more passes. Eventually the wax will stop gumming up the paper which tells me it’s removed. I let it sit for another month or so to let it dry just in case there is remaining moisture. If there was still moisture in the wood it will warp and check during this time. If it still looks good I start with the shaping, starting with a few more passes on the sand paper just to be safe.
This has worked fine for me. I’ve made 2 hill style bows with a flat riser, the entire back side of which was covered in wax prior to glue up, and they are solid and have lots of shots through them.