Does completing a tree (In order to unlock the Ultra) mean having all moves of that tree unlocked? And if so, does using the Bard class to gain aspect moves of two opposing aspects lock you out of getting either Ultra?
Generally yes, completion does mean having all moves of that tree unlocked. This is mainly used for "more important" templates like the eeries and magic templates.
For classes and aspects in particular, though, the semi-official Serverstuck Ruling is that you do not need every single move from your aspect in order to get the aspect ultra. For the purposes of Serverstuck, you only need 10 moves from a combination of your class and aspect in order to gain your aspect's [Ultra] move, which also applies to your class' [Ultra] move! If you're playing with SnS 6e offserver, you can change how the Aspect Ultra completion works as you see fit. The general idea there was just to reflect how classes and aspects both contribute to your character Becoming Their Archetype, but asking someone to take a whopping 13 moves to make that happen is. A Lot.
For the BARD class in particular, the moves they take from their opposite aspect do not contribute to their aspectal ultra! The Bard class as a whole is oriented towards gambling, risk-taking, and pushing limits until you push too far. Their ability to steal from the opposite aspect reflects this:
Additionally, you can’t unlock the opposite [Aspect] [Ultra] like this and [Aspect] moves of your opposite [Aspect] do not count towards your completion for your true [Aspect] [Ultra], you silly billy. - from the Bard [Unlock] move, TRAGICOMIC MASK
How far are you willing to neglect your own aspect before you lose sight of it entirely? They're still deeply rooted in their original aspect, but it is up to each bard whether they learn to work within their aspect or reject it entirely.
- Witch, Lead Developer for Subgrubs and Snazzards and for Serverstuck