That's right. Sometimes there is a lot of overdubbing of parts involved.
In Como Estais Amigos for example, it sounds like Janick recorded 2 lead guitars for the middle section, while Dave played rhythm:
3:13 and onwards it's also Janick playing a riff with a rather sharp tone, while he also solos at the same time, while Dave is playing power chords. That was unique for just that song, so I think there could have been some unusual parts recorded on Senjutsu as well.
I still think it's Dave (and Adrian) playing that part in Hell on Earth and not Janick though, because of the smooth neck pickup sound and the delay you can hear. I can hear 2 rhythm guitars too, when I listen with headphones - I believe that they recorded 4 guitars totally on this part.