You can put both fortune and silk touch on a tetra pickaxe. When doing this the tool will apply the last enchantment put in.

When you first put fortune and then silk touch on a Tetra tool, mining redstone or coal ore will give XP with silk touch.

If a tool has both silktouch and fortune then silktouch goes first if it's possible to silktouch the block. So in most cases it makes no sense for a player to apply both. But I still like the idea of players being able to apply them both.
The silk touch still dropping xp is a big issue, I've completely missed that and I'm not sure how to fix it yet :/.

Figured it out. Fixed in 24fb62e, available once 0.17.1 gets approved.