Well, on the topic of "hands over chest", that could be explained away by the fact that both entities have the appearance of topless women, and there's only so many ways a topless woman can be presented in a PG-rated video game. :P

Aside from that, though, I acknowledge that there's some resemblance between Seraph Ultima and the image of presumably-Hydaelyn from the Shadowbringers artwork. Aside from the crossed arms, both have wings (Hy's being distinctly more angelic, while Ulti's are bony and skeletal) and both have some kind of feathery protrusions on their heads. I think it's too soon, though, to presume that the two are the same kind of entity - or, even if they are, that it is necessarily case that both have the same kind of incomprehensible morality.

It's important to consider that Seraph Ultima is explicitly otherworldly, why Hydaelyn is so worldly that she literally IS the world. Ultima somehow wound up transported to Hydaelyn, a world alien to her, and was immediately made the subject of worship by humans. It's all she's ever known of them, and came to accept them as beings whose sole purpose is to worship her and ask for favors. The first people she met who did NOT offer her worship instead fought and imprisoned her, so it's not too surprising she reacted with hostility when more such entities appeared. Heck, it's notable that when we first encountered her, she attempted a PEACEFUL resolution, first - she offered gifts, and presented herself for worship.

Hydaelyn, on the other hand, knows humans inside and out; they've lived upon her for many thousands of years, and she's seen every aspect of how they are born, live, and die. Even if we nonetheless imagine that her concept of morality is different from that of humans (which, itself, postulates the ludicrous assumption that humans some kind of universal concept of morality), it's a big step to assume that hers is incompatible with ours. Alien = cannot be trusted is pretty much the definition of xenophobia.

On the topic of Hydaelyn and Zodiark once being a single being, though... I've had that as a theory for a while, now, but has it actually been confirmed? When did that happen?