Can I dry-brine a turkey crown while it's defrosting?
In summary, yes, you can dry-brine while thawing.

The effect will proceed no faster than the turkey thaws, as the diffusion of the salt cannot proceed into frozen meat.

I cannot recommend thawing at room temperature, which is not one of the four safe thawing methods.  

Instead, you should place your turkey crown on a rack over a tray, and salt it liberally, including any other herbs or spices you choose (although these flavors will remain at the surface).  Then place it into the refrigerator for 24 hours or more.  You don't really need three days as indicated in the recipe linked in the question, although it will do no harm to let the turkey sit longer.  The amount of salt you apply is finite, so you are not going to "overbrine".

Don't cover it or uncover it for the last 24 hours of resting time; the open air circulation will encourage some drying of the skin and giving you a crispier result.