Can I dry-brine a turkey crown while it's defrosting? At the suggestion of certain knowledgeable parties, I plan on dry-brining my turkey crown for Christmas dinner this year. However, I will most likely be buying a frozen crown, so I'm wondering what the timing should be like. 

I've heard that you can dry-brine while defrosting, but I can't find any details. I'm thinking that I should let it partially defrost before salting, letting the outer part of the turkey soften a bit. The joint will be about 2.5kg (5.5lbs), so will take about 10 hours to defrost in a cold room (boy does my kitchen fit this description). I'm thinking perhaps salting 3 hours into defrosting, letting it fully defrost, then placing it in the fridge overnight - I know dry brining should usually be longer, but this is a relatively small joint and I'd rather not give my guests massive food poisoning as a Christmas gift.
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.