Random Item Skyblock

Sadly no. Although I would love to add them eventually, but to my knowledge it's not possible at the moment. Plus it'd require a full rework of the randomizer.

Thanks for playing! If you end up having any other issues in the future please let me know!

Yeah, I'll fix it as soon as possible.
Edit: The update that fixes it is currently under review by MCPEDL, it should be published by tomorrow or later today. (Discord downloads are already fixed).

Replacing the Addon with the updated addon won't break anything at all, I'll make 100% sure of that before I release a new update publicly.

I can look into adding a boss bar, although I can't guarantee anything due to the limitations on Bedrock Behavior packs (and also just my minimal information on the topic).

As for your second question, I'm pretty sure the ominous vault (and key) can be received, but I'll check later today.
Edit: Sadly, Ominous Vaults cannot be given using the /give command, or even found in the creative menu, therefor I cannot put them into the Addon.

Thanks for playing! And yes, I will be updating this when new Minecraft updates come out. (Although it could be a few weeks after the Minecraft update when the update for this comes out.)

What do you mean?

Most likely, but I haven't tested so I'm not entirely sure.
Edit: I didn't fully understand the question, it won't be able to give you the items with the randomizer, but you could still go on creative and get the items.

Thank you!