I don't think the vocals sound even remotely alike. Ghost's vocals are too soft around the edges.

http://www.youtube.com/watch?v=bdJCvK08z1Y
http://www.youtube.com/watch?v=twMCPzY6IZg

They're not revealing their faces here. There's a blatantly apparent reason why all of the ghouls look like Phil Anselmo throughout the years, because the article is an interview of Ghost done by Phil. I'm fairly certain that is whats going on here.

There's a wannabe Gypsy vibe in the vocals from time to time, especially on Elizabeth, but as you said, incredibly thin and weak. Infestissumam vocals are even weaker.