Apologies if this was asked before, but can Galadriel (ally) put an attachment into play onto an otherwise non-legal target? Probably not, but I would like hard confirmation.

Do you have an example? Many attachments are worded "Attach to ___", and Galadriel (or Vilya, for that matter) won't get around such a condition. So no cheating Burning Brand onto a non-Lore character.

You could get Lembas or Ent Draught into play without their usual conditions, though.

So no cheating Burning Brand onto a non-Lore character.

That was exactly the example I was thinking of.

If you could, that mean you could attach anything to... anything. I mean, if you can ignore the "attach burning brand to a lore character", then why not attach it to a leadership attachment?

With this, you can easily conclude it doesn't bypass the "attach to" but can bypass "play only if..."