Yeah sure it will work but I personally dislike the idea of just claiming address space without proper coordination
If you want IPv6 just go to he.net and get a prefix. It is very much supported by OpenWrt.
This Yggdrasil is experimental and not meant to be a tunnel broker for IPv6.
I never used Yggdrasil myself, but it seems there is proper support since 21.02. There is even a special Luci App for this. Install Yggdrasil on OpenWrt. Maybe if you installed (all) the yddrasil package it will work? (again I never used this, but installing the Luci app might install something that you are missing for it to properly work).