I just found out how to add greatwood and silverwood logs to the whitelist for the 1.8.9 version of Better Foliage
It is a bit confusing that they're named planks when they in fact are logs, but nontheless, this works:
Taint logs and taint geysirs seem to be a bit more elusive, but if/when I manage to add them to the whitelist I'll let you know
While I'm at it, does anyone know how to add vanilla Minecraft blocks to the log whitelist? I'd like to add giant mushroom stems, hay bales and quartz pillars.
Guess I should've updated my situation: with the latest version, Thaumcraft's Silverwood and Greatwood logs work as intended. Only had the problem of the corners of blocks underneath the logs being kinda dark without Smooth Lighting. Nothing that putting it to Minimum didn't solve