I'm another person who had been following Sunken Veil since its inception as a fan game and from what I've seen, both sides are suspect.
I bought Salvor Deep soon after it released and ever since have checked Delusria's twitter, this itch.io page and the game's Steam discussions daily for any updates or news. Same goes for Sunken Veil; ever since the first posts on reddit, I've checked the dev's reddit account daily for updates and news.
Delusria should have been aware of Sunken Veil since its dev told very early in reddit comments back in June that he allegedly had had Delusria's go-ahead for the remake. Whether he ever got a permission for a larger scope reimagining is another matter.
There also was a comment here on itch made in August where someone asked if Delusria knew about Sunken Veil. Delusria answered yes. The post was deleted recently, which is suspicious.
If at any point Delusria wanted to denounce the project for not having his permission, he could have done so. Yet publicly, he had chosen to let it be. And now that Sunken Veil's public demo got released, his only public assent to knowing about the game (to my knowledge) vanishes and he's acting surprised that a remake-turned-fan-game is similar to its originator.
The Sunken Veil dev could have been lying too, for all that I know, and all this is hard to prove now that most evidence has been deleted. But I don't think Delusria has been completely honest either.