You are correct about Tortoise in that it is too strict.
I looked through their code and they have written their own patch
program which keys off these Index: lines
http://tortoisesvn.tigris.org/svn/tortoisesvn/trunk/src/TortoiseMerge/Patch.cpp
I think it could go either way as to if git-svn creates a different
format patch or tsvn accepts multiple formats, but I anticipated
git-svn would be easier to extend so I started here.