I'd be fine with it if it's in the white bottom part of a page and somewhat stealthy too.
Credits pages work well but I understand some aggregators delete them. Watermarks on the art just ruins everything.
About what said Teddy, your edit's right, it wouldn't hurt the scanlations team from other languages who translate from EN->their language since they'd ask the original scanlation team (and if they don't, well... they'd deserve having a watermark on the face). Which is bad a thing to do but sometimes, there's just no other way to have it available in your language when you don't know anyone knowing that language AND willing to TL.