In general, legally it may be acceptable in certain circumstances. For example, if it's a work of pure fiction and the name change is clearly part of the fictional world and not causing any harm to the real artist. Ethically, it's not so straightforward. If the novel is using the artist's new 'fictional' name to make some sort of statement or tell a story that has no negative impact on the real artist, it could be seen as okay. But if it's done without any consideration for the artist's identity and how it might be perceived, it's probably not ethical.
It can be a complex situation. Legally, if the artist is a public figure and the use of their name change doesn't defame or mislead in a way that violates laws, it might be okay. Ethically, it depends on the context. If it's for creative purposes like creating an alternate reality in the novel and not meant to harm the artist's reputation, some may consider it acceptable. However, if it's done to misappropriate the artist's identity or for malicious reasons, it's not okay.