Just as the title asks. I'm curious; I haven't noticed any blatant similarities, only small ones, like a Dwemer Centurion station there, some gears here. So; are connected, or each separate?

I don't know if there are multiple Deep Venues in Skyrim or if it's just Blackreach.

I spent an Hour or so exploring blackreach and from what I found there's more ways then just the 1 to get down there so I'd say it's the same 1.