Who in their right mind would accuse them for tracing, when their job is to trace old art? Of course the concept material is fair game under these circumstances!
I would, when the outcome is shitty. If an artist doesn't trust his own skills enough and instead end up tracing someone elses lines that doesn't even fit - why should we trust that artist? It's not strange that the akuma mouth look weird when someone just traced a head from another image and just tried to redraw some of it.
Using the original sprite to get the overall pose down is fair game, but from there they should redraw the entire thing to make it work, tracing odd bits and pieces from different source simplys doesn't work.. and we all know it. Also, why not let Edayan do the art if Udon just end up tracing her stuff anyway?
Like someone at neogaf said:
I don't want to get into this debate...but my POV is that if you're doing an HD remake, adhere to the same sprites used in the original. To take different parts of art (even if it's official art) to stitch up a Frankenstein is a half assed way of doing HD sprites.
New pic of Ryu!

Don't worry guys, it's all officially sanctioned SF art, so it's all good. 