In Curse of Strahd, how does Dispel Evil and Good's "Dismissal" option affect undead not native to Barovia?

Question

Background

In Curse of Strahd, the NPC

Rictavio (p. 238)

has the spell Dispel Evil and Good. It has the following function, similar to the spell Banishment:

Dismissal. As your action, make a melee spell attack against [...] an undead you can reach. On a hit, you attempt to drive the creature back to its home plane. The creature must succeed on a Charisma saving throw or be sent back to its home plane (if it isn’t there already). If they aren’t on their home plane, undead are sent to the Shadowfell, [...]

Note that as written, this implies that there exist undead that aren't native to the Shadowfell, but that they go there (rather than their home plane) if they are not on their home plane when they are Dismissed. (Otherwise, it would say, "If they aren't already there, undead are sent to the Shadowfell".)

However, note also that Barovia is part of the Domains of Dread, which are a demiplane within the Shadowfell.

As the NPC's most powerful spell, it seems like this ought to be of some use to them (and other aspects of the spell do indeed make it useful). But the presence of Barovia within the Shadowfell may limit its effectiveness.

Questions

It is clear that for an undead native to Barovia, nothing would happen; the Dismissal would fail.

1. For an undead not native to Barovia, would 'sending it to the Shadowfell' also result in failure? Or could it be forced from the Demiplane of Dread and deposited in the greater Shadowfell?

2. What undead within the adventure are not native to Barovia?

Zombies created by Strahd from Barovians seem likely to be natives of the demiplane itself.

Strahd himself was born on the Prime - but I would argue that his pact with the Dark Powers has made him a native of the Barovia. He is the Ancient, he is the Land.

There is a group of vampire spawn who are explicitly said to be former adventures Strahd lured to his realm and then made undead once they arrived. In this case, would Dismissal treat them as neither native to Barovia nor the Shadowfell? Is the home plane where the creature / soul is from, or where it became undead?

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Related

• What is the connection between the Shadowfell and Strahd/the plane of Barovia?
• What does the Banishment spell do inside a Demiplane?
• What determines a creature's native plane for the Banishment spell?
• If I cast the Banishment spell on myself while in a demiplane, where exactly do I exit?
• Can you cast banishment on yourself?
• Can I permanently banish a devil from one layer of the Hells to another using the Banishment spell?

Answer 1

You cannot leave Barovia

Curse of Strahd describes Alterations to Magic in Barovia as follows (CoS, p. 24):

No spell—not even wish—allows one to escape from Strahd's domain. Astral projection, teleport, plane shift, and similar spells cast for the purpose of leaving Barovia simply fail, as do effects that banish a creature to another plane of existence. These restrictions apply to magic items and artifacts that have properties that transport or banish creatures to other planes. [...]

Even undead that are not-native to Barovia can never leave, willingly or unwillingly. Dispel Evil and Good would simply fail.