Either forge:*/aluminum needs to be added to the Gregtech Aluminium stuff or forge:*/aluminum should be added to the All the Ores Aluminum stuff otherwise AlmostUnified will not unify them and their recipes.

Adding one tag to another is not a sufficient fix because recipes will still use the tag that is no longer in use.
But Almost Unified has a feature called TagOwnerships that can take care of that.

But I guess that will break the Gregtech progression.

It does which makes the choice of what to do here somewhat difficult, though the progression is somewhat broken already since the config is spawning vanilla ores like normal, I guess it's really down to how you want the pack to progress, either focusing on gregtech or not

Aluminum is still very early in the Gregtech progression, so unifying them isn't going to break Gregtech.