I don't see why, but currently he can with his Warp Star which he summons or creates.
Can it travel inbetween 4D Brane Worlds? While I don't see universal/dimensional travel that can do such on his profile, I'll take your word for it.
Kirby still scales to Dark Nebula and Drawcia, so who has the AP & dura advantages here?
Doremy is on a high end 4-A, capable of creating dozens of dreams at once, and even a single one of them can contain several stars and nebulae, of which she can nuke casually. It's not too much of a stretch to say that she can go much further in non-spellcard fights. She also manages the entire Dream World, which has all the dreams of all living beings on the Earth and the Moon, and being able to manipulate dreams, its implied she can manipulate all of it.
Also, not quite sure if Doremy can be beaten through transmutation. Her Low Godly regen is more than just regen; since her body is pretty much meaningless, her true self being her disembodied "mind". If her current one is transmuted she can simply regenerate a new one.
As for Empathic Manipulation and putting her to sleep, it should also be noted that versatility means someone is less likely to use certain powers, even if they're bloodlusted (and a bloodlusted combatant always goes for the most effective method first, altho both combatants do not have prior knowledge here at the start of the fight). Kirby also has powers that are better suited for combat than empathic manipulation and sleep manipulation, such as transmutation.
As for danmaku, it's been answered previously; Touhou is on a whole nother level compared to most other franchises when it comes to danmaku (even in casual, friendly play) and Kirby's ability to reflect danmaku can be countered with forcefields.
Finally, how good is Hypernova's void manipulation?