The Rhinelander boats I've worked on had galvanized steel fasteners and have been relatively easy to remove. As I mentioned, Shell Lake's are a different story....both boats and canoes were a genuine PITA.
I've worked on a couple Peterson Bros. and I recall steel there, too. The only Tomahawk boat I ever worked on was a replica and it was brass.
The Thompson's I've worked on have been brass, with the exception of the nails. It seems to me that on Thompson rowboats they were assembled by nailing, then screws were installed. It's the only reason I can figure that you find a bunch of small nails in Thompson boats. Thompson canoe have been all brass except for the steel finishing nails throug the gunwales.